Expert Systems With Applications 190 (2022) 116180 Contents lists available at ScienceDirect Expert Systems With Applications journal homepage: www.elsevier.com/locate/eswa Review Dynamic Programming algorithms and their applications in machine scheduling: A reviewβ© Edson Antônio Gonçalves de Souza a ,1 , Marcelo Seido Nagano a ,∗,2 , Gustavo Alencar Rolim a,b ,3 a Department of Production Engineering, São Carlos School of Engineering, University of São Paulo, Trabalhador São-Carlense 400, 13566-590, São Carlos, SP, Brazil b Department of Industrial Engineering, Technology Center, Federal University of Ceará, Campus do Pici, 60455-900, Fortaleza, CE, Brazil ARTICLE INFO Keywords: Scheduling Dynamic Programming Survey Exact methods FPTAS ABSTRACT This paper aims at presenting a compilation of state-of art references in which dynamic programming (DP) and its variants have been applied as a solution methods for the deterministic machine scheduling problems. Overall, 183 articles have been gathered and their segmentation was carried out according to the machine environment that characterized the problems addressed by the authors and ultimately, the objective functions that were intended to be optimized. Additionally, we standardized the information provided by each article by presenting the problems discussed by the authors, comparisons between previous works on the same problem (if it was deemed necessary), the algorithms’ complexities and an extension of methods to computational experiments (in case they have been stated). Finally, at the end of each section we furnish a discussion on the main contributions of DP to the each environment and also suggest some further applications of DP to machine scheduling problems, thus showing the potential resources that can be derived from the method in terms of theoretical/practical approaches. 1. Introduction Pinedo (2012) defines machine scheduling as the allocation of machines to a set of jobs whose objective is to establish the ordering that returns an optimal value for a given objective function. All these functions are usually denoted as criteria or performance measures and they are often described as time functions. Although this may seem a theoretical description of the problem, one must acknowledge its relevance, since it is related to several manufacturing scenarios and the optimization of such problem and variations of it are one of the pillars to place a company ahead in terms of competitiveness and efficiency regarding the production process. Fuchigami and Rangel (2018) describe thoroughly the applications of machine scheduling in several segments of industry, such as chemical, printed circuits, clothing, iron and steel, pharmaceutical and furniture, among others. Their analysis is recent and therefore, it can be accurate about the trends in machine scheduling over the last 20 years. An interesting fact of their research is the discussion of the methods that have been currently employed in the solution of the various problems related to scheduling and from a general standpoint, one can notice that 71.19% of the articles gathered cover heuristics and metaheuristics as solution methods. This leads to a much smaller contribution of exact methods and, even though the authors have only taken into account MILP, the participation of other methods cannot be compared to MILP, since it is one of the most common methods when contrasting performances among algorithms. Recently, a review presented by Tomazella and Nagano (2020) lists articles in which Branch and Bound (B&B) is exploited as a solution method for the flow shop environment with numerous evidences that this method, only for this flow pattern has been repeatedly employed. The same can be stated for less complex environments (e.g. single machine and parallel machines). However, when comparing the shares of MILP and B&B with other exact methods, it is noticeable that the former are recurrent options for the authors, even when being programmed in order to verify the efficiency of some non-exact methods and therefore, the use of other exact methods became less frequent over time, as it is the case of Dynamic Programming (DP). β© This document is the result of the research project funded by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES, Brazil. ∗ Corresponding author. E-mail addresses: edags90@usp.br (E.A.G.d. Souza), drnagano@sc.usp.br (M.S. Nagano), gustavo.rolim@usp.br (G.A. Rolim). 1 Researcher. 2 Co-ordinator. 3 Co-author. https://doi.org/10.1016/j.eswa.2021.116180 Received 1 March 2021; Received in revised form 21 September 2021; Accepted 29 October 2021 Available online 12 November 2021 0957-4174/© 2021 Elsevier Ltd. All rights reserved. Expert Systems With Applications 190 (2022) 116180 E.A.G.d. Souza et al. The foundations of DP can be traced back to the fifties and the first topics related to it are found in Bellman (1952) with the introduction of a class of problems whose aim is to seek an optimal set of choices which, in turn, would lead to an optimal solution. Such class had been originally presented for an stochastic framework and the author focused on outlining the Existence and Uniqueness Theorem for the problem described and its relation to a functional equation. A subsequent work is developed in Bellman et al. (1954), which extended the previous notion of probabilistic nature to the deterministic case and then, consolidated DP as an exact method used to solve optimization problems. Furthermore, the definition of DP is presented and according to the authors it can be defined as a method that divides an original problem into sub-problems of smaller dimensions by choosing, at every step, the set of decisions that returns the best result in terms of a given objective function. Such function is essentially modeled via a recursive relation (functional equation) that will ultimately generate the optimal solution for the original problem as previous solutions are aggregated. Hereafter, the communication between DP and several classic problems of Operations Research has been established. Held and Karp (1962) are probably one of the most revisited authors regarding this connection and they show how to employ DP to a general scheduling problem by developing a recursive relation that is dependent of time and whose objective is to obtain the sequence that minimizes the time the jobs remain on the system. Although the resources used in this paper might be outdated, it is deemed a stepping stone for DP and machine scheduling, once it is able to demonstrate its applicability to such problem and originate derived methods of DP that have enabled improvements for particular scenarios over time. The premises for employing DP are completely compatible with the structure of machine scheduling problems, once the problem of finding an optimal sequence can be partitioned into sub-problems that stores partial sequences until the original problem is solved and the value of the objective function can be obtained through a specific functional equation. Throughout time, DP has been diversified in scheduling and, despite not being the most applied method regarding this problem in Operations Research, its contribution can be considered substantial to the development of the machine scheduling field. Some of the contributions are: development of polynomial time algorithms (Moore, 1968; Potts & Van Wassenhove, 1982) that are still widely applied in contemporary approaches for scheduling problems, methods to reduce the state–space inherent to the DP recursive relations (Baker, 1977; Lawler, 1977; Schrage & Baker, 1978), theoretical background for generation of a large class of fully polynomial time approximation schemes (Woeginger, 2000), creation of methods derived from the original DP features (Ozolins, 2019b; Tanaka & Fujikuma, 2012), among others. This paper aims at compiling state-of-art references that relate Dynamic Programming and machine scheduling to motivate researchers that are interested in studying the connection between these two topics or those that intend to analyze the evolution of DP, its achievements and potential capabilities. Despite DP being considered a method that might be strongly associated with issues especially for NP-hard problems, as it is the case of most of scheduling literature, one of the objectives of this paper is to show the applications of DP via derived methods, which may include approximation schemes and other efficient heuristics. With that said, we can demonstrate the branches of DP in scheduling and their importance for future perspectives. We also attempt to associate complexities regarding the problem and the algorithms whenever it is given, once those are indicators of improvements in the tractability of combinatorial problems. Furthermore, the paper includes the most recent applications of DP to develop either theoretical analysis or practical algorithms. It also presents the last trends of DP as well as the gaps in the current literature. Lastly, this paper suggests promising methods that might be suitable for problems that have not been widely explored or alternative solutions to the development of the field. We structure the paper as follows: Section 2 introduces formally the concept of DP with the main elements that are intrinsic to it. Section 3 encompasses the general framework of the paper by presenting the methodology applied for this research as well as the notations that will be used throughout the review. From Section 4 to Section 8, the papers regarding single machine, parallel machine, flow shop, jobshop and open shop environments are introduced in a concise manner, respectively. In addition, the subsections are distributed according to the objective functions that can be grouped due to their akin nature with considerations being provided at the end of each section. Section 9 encloses concluding remarks and the direction of DP regarding further studies in machine scheduling. 2. Dynamic programming Whenever we conceive the idea of optimal solution, the first method that often rises is the explicit enumeration or brute force method, which can be thought of as counting over every possible solution a given system can provide. A variety of problems in Operations Research are formulated under a combinatorial nature (e.g. machine scheduling, TSP) and therefore, each different ordering represents a distinct combination that can be evaluated as optimum according to the value of the objective function. From either mathematical and computational standpoints, this method might be infeasible because such approach reaches factorial complexity (π(π!)) and consequently, it solves only small-sized instances. Dynamic Programming and Branch and Bound methods can be classified as implicit enumeration methods and their structure is usually based on finding the optimal solution by not analyzing every possible combination and, for this reason, the overall complexity associated to a given method is reduced. A common feature that can be found in both methods is the partition of the original problem in sub-problems that contain a smaller dimension. Once every subset reaches the number of elements of the original problem, usually denoted by π, the problem is solved and the optimal value is found for the objective function. Before fully comprehending the concept of DP, it is relevant to introduce some preliminary elements that are common to either simple or complex formulations regarding such method. These concepts will guide the reader throughout the next sections and they represent the core of DP that should be unfolded into mathematical and theoretical analyses. Hence, such terms can be detailed as follows: • Stage (π): Associated to the given level a sub-problem can be found. Usually designates the dimension or cardinality of decision making variables that have been allocated. • Control/State (π’π ): A control is the decision making variable associated with stage π, i.e. the variable that represents a decision that will be allocated at a given stage π. The set of decisions at stage π are denoted by ππ , such that ππ = {π’1π , … , π’π‘π }. • State variable (π₯π ): Real-valued function that stores the value of the objective function for a given state π’π that is chosen to aggregate the solution set at a given stage π. • Policy (πΌ): Denotes the set of states that have been selected at each stage, i.e. the set of feasible solutions that is allowed at a given stage. Once optimal states are of interest here, one can define an optimal policy as the set of optimal states that are adopted at each stage and, consequently, return the optimal solution. Clearly, this set of concepts might be enlarged to adjust to a specific problem’s requirements, however, these four definitions will be common to every problem involving DP and once they have been established we are able to formally introduce a concept for DP. Despite Bellman et al. (1954) introducing a consistent mathematical formalism for DP’s definition, a simpler and formal characterization is given in Bellman (1966) in which the author defines DP as a method 2 Expert Systems With Applications 190 (2022) 116180 E.A.G.d. Souza et al. Table 1 Processing times and description of function βπ (πΆπ ). dedicated to the investigation of multistage decision processes that demand a sequence of decisions over time. These decisions can be accounted as sub-problems solutions and this is one of the premises that confirm the viability of applying DP to a given problem. Over the years more robust definitions have emerged in literature. In the present days, a definition that seems to be conventional among authors is the one seen in Bautista and Pereira (2009). The authors state that DP is a technique that partitions the original problem into smaller sub-problems, which are solved sequentially until the original problem is solved through aggregations of solutions obtained in the previous states. Additionally, it is also defined as a multistage graph πΊ(ππ , π ), with π being the transitions that occur from a stage to the next. Note that ππ corresponds to the set of vertices of the graph that can be stored at the same level and π is analogous to the edges of a graph. The second premise that governs the proper use of DP to a problem relies on the formulation of the problem via a recursive equation, which is essentially a functional equation. Mathematically, a general model to describe DP can be represented as follows ππ (π’π , ππ ) = min {ππ (π₯π , ππ ) + ππ−1 (π’π−1 , ππ−1 )}, π’π ∈ππ π = 1, … , π βπ (πΆπ ) 4 3 6 πΆ1 + πΆ12 3 + πΆ23 8πΆ3 π∈{π⊕π} ∀π‘ ∈ π. π∈{π⊕π} (3) In order to find the minimum sum of this general function of completion times, we need to find the best sequence that can yield this sum. Let us consider the data in Table 1 for a 3-job problem: We can calculate the allocation of the jobs at the first stage by using the initial condition. Since each job is placed in the first position we obtain (1) π1 (1, ∅) = 4 + 16 = 20, π1 (2, ∅) = 3 + 27 = 30, π1 (3, ∅) = 8 × 6 = 48. At the second stage we start calculating via the recursive equation π2 (2, {1}) = min{β1 (π1 + π2 ) + π1 (2, ∅); β2 (π1 + π2 ) + π1 (1, ∅)} = min{56 + 30; 346 + 20} = 86 π2 (3, {1}) = min{β1 (π1 + π3 ) + π1 (3, ∅); β3 (π1 + π3 ) + π1 (1, ∅)} = min{110 + 48; 80 + 20} = 100 π2 (3, {2}) = min{β2 (π2 + π3 ) + π1 (3, ∅); β3 (π2 + π3 ) + π1 (2, ∅)} Theorem 1. An optimal policy has the property that whatever the initial state and initial decisions are, the remaining decisions must constitute an optimal policy with no regard to the state resulting from the first decisions. = min{732 + 48; 72 + 30} = 102. The last stage is calculated by assembling the jobs in one set. Therefore π3 (3, {1, 2}) = min {β1 (π1 + π2 + π3 ) + π2 (3, {2}); β2 (π1 + π2 + π3 ) Essentially, the principle correlates the optimization of the original problem and the sub-problems. In other words, if the optimal policies have been previously selected for the preceding stages and optimal policies are assumed for the remaining ones, we guarantee that the optimal solution will be found for the initial problem. Moreover, the principle indicates that remaining states are dependent only on the current stage rather than the initial ones. Regarding the inner methods that are bound to the DP approach, it is valid to mention that throughout literature references, extensive records have been found involving forward and backward recursion. The first type is characterized by placing the initial condition at stage zero and gradually aggregating the states so as to obtain the objective function at the final stage π. The second one works analogously, however we consider an initial condition at the last stage and the objective function is achieved at the first stage. Variations of those may be also found, however their usage is not often employed and therefore, will not be mentioned. In order to apply the concepts introduced here, we present an example of dynamic programming applied to a single machine scheduling problem aiming at minimizing a general function. + π2 (3, {1}); β3 (π1 + π2 + π3 ) + π2 (2, {1})} = min{182 + 102; 2200 + 100; 104 + 86} = 190. The example shown above is actually a generalization of functions that deal with completion times (e.g. total tardiness, earliness, among others). Despite displaying only the value of the minimum sum, it is also necessary to be thorough in this analysis and present the sequence that yields such value. As we can notice, this is a forward DP mechanism because an initial condition is set at the first stage rather than the last one and the sequence can be obtained by using backtracking analysis derived from the optimal value. We may notice that the minimum was attained by adding job 3 to π2 (2, {1}) and the minimum in this set was originated from job 1 being placed after job 2. Therefore, the optimal sequence is given by 2-1-3. After confirming the advantages of DP approach, the reader might question the disadvantages of such method for several problems, mostly those that involve an allocation process. Bellman and Lee (1978) explore the use of several functional equations for specific problems in Operations Research and they state that as the number of state variables increases, so does the computational effort in terms of memory requirements and CPU time and it can be justified due to the recursive nature of the functional equations that compose the premises of DP. Such effect is known as Curse of Dimensionality and it is clearly one of the reasons related to the limited use of this approach to solve problems in the optimization field. Over the years, due to this disadvantage and the fact that most scheduling problems are NP-hard, DP has not been a constant choice of authors in the field as it can be seen for other exact methods and Branch-and-Bound, Mixed Integer Linear Programming (MILP), among others. Due to this disadvantage and the fact that most scheduling Example 1. Let π be a given job such that π ∈ π½ that must be processed on a given machine. The interest of the scheduler is to minimize the sum of a function βπ , such that ππ = βπ (πΆπ ), with πΆπ being the completion time of job π on the machine. By Graham’s notation, this ∑ problem can be denoted by 1β₯ ππ (πΆπ ). According to the definition previously described we need a recursive relation for calculation the objective function and an initial condition as an input for the recursion. Therefore we define the initial condition as ∀π ∈ π½ ππ 1 2 3 and the recursive relation is given by { ( ) } ∑ ππ ({π}, π) = min βπ ππ + ππ−1 ({π‘}, π − {π‘}) , Eq. (1) characterizes the functional relation that represents a recursive mechanism related to DP. The function ππ (π₯π , π’π ) indicates the cost associated to the allocation of state π’π at stage π and the function ππ−1 (π’π−1 , ππ−1 ) denotes the optimal objective function for the previous stages and one can see that it is the main term related to the recursion effect. As a consequence of this fact, it is worth mentioning that Eq. (1) is only one of the several types of formulations designed for DP functional equations, however all of them are derived from a common factor known as Bellman’s Principle of Optimality, which is stated as follows. π1 ({π}, ∅) = βπ (ππ ), π (2) 3 Expert Systems With Applications 190 (2022) 116180 E.A.G.d. Souza et al. of articles that each subsection contains. For, example, as we shall see on the next section, the number of tardy jobs criterion presents a considerable amount of papers with regard to the single machine environment and, therefore it is disjointed from the classic due date related criteria subsection. The two last determining conditions that have been set as a filter were the relevance of scheduling, i.e. whether scheduling was the main topic on that paper or just included as an intermediate process for another part of the supply chain, and the nature of the scheduling problem according to their deterministic or stochastic formulations. Hence, for the first filter, the majority of papers that have been gathered were verified through that analysis, except those that explored the batching constraint, which have shown stronger features towards other systems such as demand forecast and allocation and transportation analysis. The second filter would include only deterministic cases in our research because the number of stochastic cases would not be significant in this analysis and also they would be scattered throughout the environments. More precisely, 219 papers linking DP and machine scheduling have been initially found from 1952 to August 2020. According to our methodology of inclusion/exclusion, 34 papers have not been considered, given that 13 of those corresponded to the stochastic approach of the problem and 21 involved batching features that would not consider scheduling as main topic. Hence, 183 articles have been included and can be subdivided in 63 papers concerning the single machine environment, 66 papers encompassing parallel machines, 32 dealing with flow shop scheduling, 10 for the job shop environment and the remaining 12 open shop scheduling. Furthermore, we have decided to summarize the information concerning each article by introducing the notations to describe the approached problems, a description of how DP has been used, the algorithms’ complexity, in case they have been provided, and lastly, results related to computational experiments, when applicable. problems are NP-hard, DP may not be a frequent choice in comparison with other exact methods. However, a great advantage of DP is the absence of the fixed formalism required by mathematical programming approaches. This enables DP to not only rewrite these other methods from its perspective but also to extend their possibilities. Additionally, since it has been perceived that this is a useful trait of DP for optimization problems in general, some authors in scheduling have been concentrating their researches in developing hybrid algorithms that combine features of DP and other exact algorithms such as B&B, Branch-and-Cut and Column Generation method. Also, due to the mutability to heuristics, some authors have also been focused on enhancing the quality of DP to already existing methods as well as the generation of new methods that have gradually proven that the Curse of Dimensionality is a disadvantage that can be overcome for larger instances if additional properties of DP are explored. 3. Notations and methodology This section is majorly part of the methodological comprehension that entails the motives related to the production of this paper. It has been divided into two subsections with the first one gathering the topics that justify the collection of articles that have been included in our research. The second subsection comprises the notations that are commonly known to the machine scheduling experts with regard to the environment, technological constraints and objective functions. 3.1. Methodology The primary concern of this research was to define its purpose based on the applications of DP to machine scheduling. After a series of discussions we decided that this paper would represent a guide for researchers in terms of the progress and the trends that have been developed for DP in the machine scheduling and therefore, we defined this paper as one of informative characteristics. Once the field is very extensive, the filtering was set according to the classic environments because by using them as keywords we would be able to cover a large spectrum of papers concerning each environment and their variations and also to gather information on correlated distributions of machines, which has defined the first separation method. The next step was to determine the most appropriate browsing sources from which the papers would be extracted. Therefore we adopted two types of sources: general and specific. The general source was Google Scholar because it usually furnishes a larger number of papers, even though some of them are not part of the previously defined scope. The specific sources were Scopus and Web of Science because their search method is more refined than that presented by Google Scholar, even though some papers might not be included in their database. Hence, the filtering process starts with selecting the papers in the specific sources and, a posteriori, overlapping those with the papers extracted from the general sources. The search for articles depended on a standardized set of keywords that can be seen in Table 2. These words were the main ones we considered because their combination has generated distinct results and the major portion of those have been included in our research. It is valid to highlight that regarding the flow shop and job shop environments, it was preferred to focus on the classic configuration of those because the contributions of DP to the variations of such environments (e.g. flexible flow shop, flexible job shop, non-permutation flow shop) have been only related to references throughout the papers. Sequentially, we have defined another segmentation within each machine environment that is relative to the objective function. In order to cover as many papers as possible and organize them with a reduced number of subsections we divided the objective functions according to their nature: classic due date related criteria, makespan and completion time related criteria, multi-criteria and additional objective functions. Clearly this configuration could be modified depending on the number 3.2. Notations A problem in machine scheduling is defined as follows: Let π ∈ πΎ be a given machine, with πΎ denoting the set of machines and π ∈ π½ be a given job, which constitutes a set of jobs π½ . The objective is to seek the best ordering of jobs that will be processed on the machines, which is denoted by π ∈ π±, such that it yields the optimal value depending on the function the scheduler wishes to optimize. The time spent by the job on a given machine is given by the processing time πππ and it is one of the fundamental parameters in machine scheduling. The other parameters that are also representative in the field are the due dates (ππ ), deadlines (π π ), common due dates (π), due window (ππ€π ) and common due window (ππ€ ). All those have a relationship with the moment in time the jobs should finish their processing and the first three parameters are set for a given value, while the remaining ones are set for a given interval. The notation introduced in Graham, Lawler, Lenstra, and Kan (1979) is still widely used in papers and books that are reference in scheduling, even though recent ones have been developed. This notation is based on three parameters as follows: πΌ|π½|πΎ. Parameter πΌ is based on the pattern flow of the problem, which can be defined as the manner the jobs flow through the production system or, in other words, the environment that defines the problem. This parameter will also be associated with the number of machines relative to the problem. Parameter π½ is related to the technological constraints in the problem. In other words, there is a constraint added (e.g. blocking) that will alter the configuration of the general problem. The last parameter, πΎ, represents the criterion or criteria to be optimized. It is necessary to understand and recognize the main elements that each parameter may assume. A detailed description provided by Pinedo (2012) of these elements is given as follows: 4 Expert Systems With Applications 190 (2022) 116180 E.A.G.d. Souza et al. Table 2 Table concerning keywords related to the scope of the research. Environment/Method Keywords description Single machine ‘‘single machine’’ and ‘‘dynamic programming’’; ‘‘single machine scheduling’’ and ‘‘dynamic programming’’; ‘‘single machine’’ and ‘‘DP’’ Parallel machines ‘‘parallel machine’’ and ‘‘dynamic programming’’; ‘‘parallel machine scheduling’’ and ‘‘dynamic programming’’; ‘‘parallel machine’’ and ‘‘DP’’ Flow-shop ‘‘flowshop scheduling’’ and ‘‘dynamic programming’’ ‘‘flow-shop scheduling’’ and ‘‘dynamic programming’’; ‘‘flow shop scheduling’’ and ‘‘dynamic programming’’; ‘‘flowshop scheduling’’ and ‘‘DP’’ ‘‘flow-shop scheduling’’ and ‘‘DP’’; ‘‘flow shop scheduling’’ and ‘‘DP’’ Job shop ‘‘job-shop ‘‘job shop ‘‘job-shop ‘‘job shop Open shop ‘‘open shop scheduling’’ and ‘‘dynamic programming’’; ‘‘open shop scheduling’’ and ‘‘DP’’ Dynamic programming ‘‘dynamic ‘‘dynamic ‘‘dynamic ‘‘dynamic ‘‘dynamic scheduling’’ scheduling’’ scheduling’’ scheduling’’ and and and and programming programming programming programming programming ‘‘dynamic programming’’; ‘‘dynamic programming’’; ‘‘DP’’; ‘‘DP’’ applied’’ applied’’ applied’’ applied’’ applied’’ to to to to to the the the the the ‘‘single machine scheduling problem’’; ‘‘parallel machine scheduling problem’’; ‘‘flow shop scheduling problem’’; ‘‘job shop scheduling problem’’; ‘‘open shop scheduling problem’’ Table 3 Common notations for machine scheduling problems. Parameter Denomination Notation Additional comments πΌ Single machine Identical parallel machine Uniform parallel machine Unrelated parallel machine Flow shop Job shop Open shop 1 ππ ππ π π πΉπ π½π ππ – – – – – – – Release dates Precedence Preemption Resumable jobs Semi-resumable jobs Non-resumable jobs Sequence independent setup times Sequence dependent setup times Sequence independent setup family Sequence dependent setup family Controllable processing times Learning effect Aging effect Blocking Constrained rejection Permutation No-wait ππ ππππ ππππ π − π(ππ ) π π − π(ππ ) ππ − π(ππ ) π π βπ ππ π ππ βπ πππ ππΌπ ππ·π π(π¦) πΏπ π΄π πππππ ∑ πππ ππ ≤ πΎ ππππ’ ππ€π‘ – – – – – – – – – – Examples of π¦: ππ , π π‘π , π₯π – – – πΎ represents an upper bound – – Makespan πΆmax πΆmax = max πΆ[π]π Maximum tardiness Total tardiness Total weighted tardiness πmax ∑ π ∑ π π€π ππ ππ = Maximum lateness πΏmax πΏπ = |πΆπ − ππ | Number of tardy jobs Weighted number of tardy jobs ∑ π ∑ π π€π ππ ππ = Total flow time Total weighted flow time ∑ πΉ ∑ π π€π πΉπ πΉπ = πΆπ − ππ Total earliness Total weighted earliness ∑ πΈ ∑ π π€π πΈπ πΈπ = max1≤π≤π {0, ππ − πΆπ } Total late work ∑ Total weighted late work ∑ π½ πΎ 5 ππ π€π ππ { πΆπ − ππ , if πΆπ > ππ 0, otherwise { 1, if πΆπ > ππ 0, otherwise β§0, if πΆπ ≤ ππ βͺ ππ = β¨πΆπ − ππ , if ππ < πΆπ < ππ + ππ βͺ if ππ + ππ ≤ πΆπ β©ππ , Expert Systems With Applications 190 (2022) 116180 E.A.G.d. Souza et al. Clearly, other functions might appear but they are derived from those that have been outlined in Table 3 or just have the converse effect (e.g. early work criteria) and therefore they are not detailed in this section. Nevertheless, whenever a new notation surfaces, we will mention them in order to clarify it to the reader. The same can be stated for the technological constraints. For further details we refer to Rolim and Nagano (2020). which are included to reduce the state space of feasible sets. It is shown that decomposition algorithms outperformed precedence ones with the most efficient one being able to solve 100 jobs problems within reasonable time. Abdul-Razaq, Potts, and Van Wassenhove (1990) compare two DP formulations based on Lawler and Schrage–Baker works and four B&B algorithms with lower bounds derived from Lagrangian, exponential, ∑ linear and state–space relaxations for the 1β₯ π€π ππ problem. The best results have relied on the B&B algorithms, especially the one with linear lower bound, which managed to solve up to 40 jobs. The DP algorithms were limited by core storage as problem sizes grew larger, despite yielding small time CPU times. Sen and Borah (1991) develop a branching scheme based on order∑ ing theorems to compare it to a DP approach for solving the 1β₯ ππ problem. Even though the comparison was not made to measure efficiency, parameters such as dispersion of CPU times and generated state space have been provided. The branching scheme presents a smaller solution set, whereas a more scattered group in CPU times. Tang, Xuan, and Liu (2007) aim at a different approach for the ∑ 1|ππππ| π€π ππ problem by proposing a Lagrangian relaxation of the model and applying a hybrid backward and forward DP algorithm for finding optimal solutions. This paper is considered a breakthrough in the field due to its capacity of assessing all precedence relationships and for also showing a faster convergence regarding the solutions for small and large sized problems. Tuong, Soukhal, and Billaut (2010) discuss general aspects from the algorithm proposed by Lawler and Moore (1969) to solve the ∑ 1|ππ = π| π€π ππ problem and some drawbacks such as the exclusion of straddling jobs are pointed out. Therefore, they propose a DP algorithm that takes into account that possibility, which is proven to have π(π2 π) complexity. Zhang, Lu, and Yuan (2010) explore the nature of several problems that include the penalty for rejected jobs as a bounded constraint (denoted here by πππππ ), which has been drawing considerable attention lately since rejection might imply reduction in costs for jobs that have larger processing times and do not alter significantly the composition of ∑ the process. The authors prove that 1| πππππ ≤ πΎ|πΏmax is NP-complete and they develop a DP formalism in which cases of acceptance and ∑ rejection are modeled recursively with π(ππΎ ππ ) complexity. In addition, a fully polynomial time approximation scheme (FPTAS) is derived for this problem Tanaka and Fujikuma (2012) develop a framework to solve several problems by improving the successive sublimation DP algorithm seen in Tanaka, Fujikuma, and Araki (2009). These improvements take into account relaxations, reduction methods and shortened connections in networks. The algorithm is able to solve optimally 80-job instances for the 1|ππ |π€π ππ problem, thus outperforming previous methods. ∑ Tanaka and Sato (2013) take interest in studying the 1|ππππ| π€π ππ by applying Lagrangian relaxation and reductions in paths generated by the precedence networks that compose the proposed successive sublimation DP algorithm. The algorithm is able to solve all 50-job instances for the problem and most of the 100-job instances. Rostami, Creemers, and Leus (2019) gather information on precedence theorems in order to develop a more efficient exact algorithm ∑ to solve the 1|ππππ| π€π ππ problem. They construct a DP algorithm with inbuilt formulations related to those theorems in order to diminish the computational effort in generation of states and compare it to that proposed by Tanaka and Sato (2013). The results were superior for the most recent method, since it could solve some set of instances that had not been solved by its predecessor and also larger ones. Mor and Shapira (2020) investigate the use of theoretical formula∑ ∑ tions in DP in order to solve the 1|ππ = π, πππππ ≤ πΎ| ππ , 1|ππ = π, ∑ πππ ∑ ππ ≤ πΎ| π€π ππ problems via computational tests and the complex∑ ities associated with them are π(ππΎ ππ ) and π(π2 ππΎ). The computational results show that good outcomes can be obtained for at most 150 jobs and a varying rate of rejected jobs within a short time for the first problem and for at most 40 jobs regarding the second type of problem. A summary of the papers in this subsection can be found in Table 4. 4. Single machine Due to its simplicity when compared to other environments in scheduling, the variations that come with this problem are abundant regarding the constraints as well as the objective functions that present potential interest in manufacturing. Therefore, experimenting on a single machine and finding solutions to tackle variants related to it may have positive impact on developing adapted methods for far more complex systems. Among those solutions, dynamic programming has shown substantial contribution when applied to single machine problems, for both classic and contemporary approaches. 4.1. Classic due-dates related criteria ∑ ∑ Lawler and Moore (1969) model the 1β₯ π€π πΈπ , 1|π, π| ππ and ∑ 1|ππ = π| π€π ππ problems as knapsack-like formulations and, based on that premise, a DP approach is obtained from a previous DP solution for the knapsack problem. In addition, the formulation is combined ∑ with a non-increasing π€π βππ priority rule for 1β₯ π€π πΈπ , a SPT rule ∑ ∑ for 1|π, π| ππ and a non-decreasing π€π βππ rule for 1|ππ = π| π€π ππ . Complexities for the first and third DP approaches are given by π(ππ) and π(π2 π), respectively. Srinivasan (1971) applies the theoretical background available on precedence relations to a DP formulation ("hybrid" algorithm) to solve ∑ the 1β₯ ππ via the principle of optimality. The tests are performed in data sets with up to 12 jobs and the CPU times results are far better than those obtained by complete enumeration and full DP approach. Lawler (1977) proposes a pseudo-polynomial algorithm endorsed by properties of agreeable jobs and a DP formulation based on the ∑ principle of optimality to solve the 1β₯ π€π ππ problem. Although some options have been offered and employed to reduce the algorithm’s ∑ complexity, the author proves it to be π(π4 ππ ) or π(π5 max{ππ }) in a worst-case scenario. Baker (1977) focuses on applying the dominance rules proposed ∑ by Emmons (1969) to find efficient solutions for the 1β₯ ππ . By coupling those rules with a DP formulation, the author manages to develop a forward recursion DP chain algorithm. For a 15-job data set the algorithm produces better results in terms of CPU times and storage than conventional DP and the one proposed by Srinivasan (1971). The comparison with a dual algorithm for a 20-job set generates better results, however the storage requirements start approximating those in conventional DP once cardinality of jobs is over 30 units. Schrage and Baker (1978) consider an efficiency aspect of the DP formulation by devising a labeling scheme in order to reduce the computational effort when storing information from a previous stage for problems with precedence constraints. The method is applied to ∑ ∑ 1|ππππ| ππ and 1|ππππ| π€π ππ problems and compared to a chain algorithm, proving that DP outperforms the chain algorithm since the former explores a smaller number of feasible sets. Potts and Van Wassenhove (1982) combine features of the decomposition properties proposed by Lawler (1977) and labeling scheme studied in Schrage and Baker (1978) in order to introduce a more ∑ powerful DP algorithm to solve 1β₯ ππ , which resorts to decomposition if a given storage threshold is achieved. The experimental sets contain data ranging from 50 to 100 jobs, which are solved within reasonable time for instances up to 70 jobs and is proven to have π(π4 ) complexity. Potts and Van Wassenhove (1987) present a series of adapted DP ∑ algorithms to solve the 1β₯ ππ problem. The authors divide the algorithms according to their precedence or decomposition properties, 6 Expert Systems With Applications 190 (2022) 116180 E.A.G.d. Souza et al. Table 4 Due-date related problems for single machine. Authors Lawler and Moore (1969) Problem notation ∑ π€π πΈπ ∑ 1|π, π| ππ ∑ 1|ππ = π| π€π ππ 1β₯ 1β₯ ∑ Lawler (1977) 1β₯ ∑ Baker (1977) 1β₯ ∑ Srinivasan (1971) Schrage and Baker (1978) ππ ) or π(π max ππ ) DP – DP π€ π ππ – DP ππ π(π4 ) DP ππ – DP π€π ππ – DP and B&B ππ – 1β₯ 1β₯ ∑ Sen and Borah (1991) 1β₯ ∑ Cheng and Ding (2000) 1|ππ (π π‘π ), ππ |πΏmax Tang et al. (2007) 1|ππππ| ∑ 1|ππ = π| πππππ ∑ 1|ππππ| Rostami et al. (2019) 1|ππππ| ∑ 1|ππ = 1|ππ = π(π log π) DP π€ π ππ – Hybrid DP ∑ π(π2 π) π€ π ππ π(ππΎ ∑ DP ππ ) DP and FPTAS – SSDP π€ π ππ – SSDP π€ π ππ – ππ Tanaka and Sato (2013) DP 6 ≤ πΎ|πΏmax ∑ Mor and Shapira (2020) 5 ππ ∑ Abdul-Razaq et al. (1990) 1|ππ | ∑ DP ∑ Potts and Van Wassenhove (1987) Tanaka and Fujikuma (2012) DP 4 – ∑ 1| DP π(π 1β₯ Zhang et al. (2010) DP π(π2 π) π€π ππ 1|ππππ| ∑ DP – ππ ∑ Tuong et al. (2010) Method π(ππ) – ππ 1|ππππ| Potts and Van Wassenhove (1982) Complexity ∑ π, πππππ ∑ π, πππππ ≤ πΎ| ≤ πΎ| ∑ ∑ DP ∑ ππ ) ππ π(ππΎ π€π ππ π(π2 ππΎ) DP DP (R). The most promising results are obtained from the R+BBDP and R+DPLM algorithms, since they can be used for solving large problems up to 1000 jobs. Lawler (1990) incorporates aspects of a preemptive EDD priority ∑ rule to a DP formulation to solve the 1|ππ , ππππ| π€π ππ and ∑ 1|ππ , ππππ| ππ . The DP algorithm is classified as pseudo-polynomial with π(ππ2 π 2 ) time complexity and π(π2 π ) space complexity for the first problem and with time complexity π(π3 π2 ) for the second, where ∑ π is the number of distinct release dates and π = π€π . The algorithm ∑ is also extended to the special case 1|ππ | ππ , producing the knapsack DP formulation seen in Lawler and Moore (1969). In Hariri and Potts (1994) a bounding scheme is presented by using state–space relaxation and job penalties dependent on DP formulations ∑ to develop a B&B to solve 1|π π | π€π ππ . The experiments range from 50 to 300 jobs and good results are obtained, provided that processing ∑ times are not too large since the algorithm is bounded by π(π ππ ) time complexity. Lee (1996) investigates a series of optimization problems involving resumable and non-resumable availability constraints. Among them, the author points that the algorithm in Moore (1968) with the inclusion of the unavailability period in the completion times solves the ∑ 1|π − π| ππ problem optimally. ∑ Dondeti and Mohanty (1998) model the 1|πΉ π, πΏπ| π€π ππ as a 0–1 knapsack problem and combine a DP formulation with a maximumweighted network path algorithm in order to solve it. The validation of such equivalence is established by lemmas based on EDD rule and modifications on the recursive relation used for building the DP algorithm. ∑ Baptiste (1999a) shows several properties for the 1|ππ , ππππ| ππ problem, which are the foundation for a DP algorithm devised for solving such problem. The author is able to reduce time and space complexities (compared do Lawler’s), respectively, from π(π5 ) to π(π4 ) and π(π3 ) to π(π2 ). Experiments to test the DP efficiency are designed for 50 and 100 jobs and solved in reasonable CPU times. 4.2. Number of tardy jobs ∑ Moore (1968) presents a DP algorithm to solve the 1β₯ ππ problem, by including SPT, LPT and earliest due date rules in its composition. It is classified as a polynomial time method with π(π log π) time complexity. A DP approach has also been found in Lawler and Moore (1969). The authors use similar mechanisms seen in Classic due-dates related criteria and resort to an earliest due date (EDD) priority rule to solve ∑ the 1β₯ ππ problem. Tardy jobs are identified whenever zero processing times are yielded from the DP formulation and its complexity is ∑ given by π(π min{ ππ , max{ππ }}). ∑ Sahni (1976) uses its previous work concerning 1β₯ π€π ππ to formulate a DP algorithm that also employs EDD priority rule. In addition, an elimination criterion is applied so as to reduce the state space by comparing tuples that include ππ and π€π . This generates a π(min{2π , ππ}) ∑ ∑ time complexity algorithm, where π = min{ π€π , ππ , ππ } + 1 tuples. The author also studies properties and presents an approximation algorithm to solve the same problem. ∑ Kise, Ibaraki, and Mine (1978) aim at minimizing the 1|ππ | ππ problem by imposing a non-decreasing restriction such that ππ ≤ ππ implies ππ ≤ ππ . The authors design an π(π2 ) polynomial time DP algorithm and validate its capacity to solve the problem. Gens and Levner (1981) design an approximation scheme to min∑ imize the 1|ππ = π| π€π ππ problem by inserting a DP scheme with a proposed modification to Sahni’s approximation algorithm so as to eliminate redundant solutions, thus delivering a smaller set of feasible solutions and π(π2 log π + π2 βπ) time complexity. Potts and Van Wassenhove (1988) develop eight algorithms and ∑ analyze their performance in solving the 1β₯ π€π ππ problem. The algorithms are obtained by deriving lower bounds from Lawler and Moore (1969) (DPLM), a LP relaxation (BBLP), a branch and bound method (BBDP) and number of tardy jobs lower bound (BBNTJ). In addition, all of them are also implemented by applying the Reduction Theorem 7 Expert Systems With Applications 190 (2022) 116180 E.A.G.d. Souza et al. Table 5 Number of tardy jobs related problems for single machine. Authors Problem notation ∑ ππ Moore (1968) 1β₯ Lawler and Moore (1969) 1β₯ ∑ 1β₯ ∑ Sahni (1976) π€π ππ 1|ππ | 1|ππ = π| Potts and Van Wassenhove (1988) 1β₯ Lawler (1990) ∑ 1|ππ , ππππ| π€π ππ ∑ 1|ππ , ππππ| ππ Hariri and Potts (1994) 1|π π , ππ | π€π ππ π€π ππ ∑ Lee (1996) 1|π − π| 1|πΉ π, πΏπ| Baptiste (1999a) ∑ 1|ππ , ππππ| 2 ∑ DP 2 π(π ) - π(π ) 1|ππ = π, ππ | π€π ππ ∑ 1|ππππ, ππ = π, ππ | π€π ππ Woeginger (2000) 1β₯ Zhang et al. (2010) 1| 7 – ∑ π€π ππ π(ππΎ Baptiste (1999b) proposes DP-based polynomial time algorithms ∑ ∑ to solve 1|ππ = π, ππ | π€π ππ and 1|ππππ, ππ = π, ππ | π€π ππ problems, respectively. By examining their properties, the author is able to prove that the first algorithm has π(π7 ) time complexity while the second is π(π10 ). Woeginger (2000) outlines a series of cases reasoning that, given some properties, some scheduling problems could provide a FPTAS by altering their DP formulations. Among them, the author suggests that, employing properties seen in Gens and Levner (1981), Sahni (1976), ∑ the DP approaches generate a FPTAS for 1β₯ π€π ππ . Zhang et al. (2010) analyze a DP formulation that depends on the makespan of early jobs that have been accepted and a total rejection ∑ ∑ penalty for the 1| πππππ ≤ πΎ| π€π ππ problem and it is bounded by ∑ π(ππΎ ππ ). The problem is categorized as NP-hard. Table 5 summarizes all the articles in this subsection. DP DP DP π(π ) π(π10 ) π€π ππ πππππ ≤ πΎ| DP with weighted network path 4 ππ DP DP B&B with DP ππ ) π(π log π) Baptiste (1999b) ∑ DP, B&B and LP relaxation 2 – ∑ ∑ – π(π π€π ππ ∑ DP Approximation with DP π(ππ π ) - π(π π ) π(π3 π2 ) ππ ∑ π(π ) π(π2 log π + π2 βπ) 2 π€π ππ DP DP 2 ππ Dondeti and Mohanty (1998) ππ , max{ππ }}) π(min{2 , ππ}) Kise et al. (1978) ∑ ∑ π Gens and Levner (1981) ∑ Method DP π(π min{ ππ ∑ Complexity π(π log π) FPTAS with DP ∑ ππ ) DP Ji, He, and Cheng (2006) formulate a DP-based pseudo-polynomial ∑ time algorithm to deal with solutions for the 1|ππ − π, ππ (π π‘π )| πΆπ problem, with unavailability in the (π‘1 , π‘2 ) interval. In addition, proof on the NP-hardness of the problem is shown and a pseudo-polynomial ∏ DP algorithm with π(π(π‘1 − π‘0 )π‘2 (1 + ππ )) is formulated. Ultimately, a heuristic procedure is also provided for the same problem. Kacem, Chu, and Souissi (2008) propose a DP algorithm, an integer programming formulation and a B&B for finding an optimal sched∑ ule regarding the 1|π − π| π€π πΆπ problem. After tests being run and comparisons being made in terms of CPU time and storage requirements among the methods, the authors conclude the DP algorithm outperforms the other two, solving instances with up to 3000 jobs. Fan, Li, Zhou, and Zhang (2011) contribute with theoretical analysis ∑ on the complexity of 1|β(π), π − π, ππ (π‘)| πΆπ , where π corresponds to the number of unavailable periods. Two DP algorithms are furnished to solve a special case when π = 1 with resumability with π(π2 (π‘2 − π‘1 )2 ) ∏ and π(π2 (π‘2 − π‘1 )2 (1 + ππ )) complexities, respectively. Furthermore, a complexity assessment is given for both scenarios and for the general case, no polynomial time approximation is likely to occur for constant deteriorating rate. Tanaka and Fujikuma (2012) also apply the modified successive ∑ sublimation DP method for 1|ππ | π€π πΆπ and obtain optimal schedules for problems containing up to 200 jobs. Li and Fan (2012) intensify the characteristics of the problems previously examined by Fan et al. (2011), however considering only non-resumable scenarios and weighted completion time. For single unavailable intervals, an π(ππ‘1 ) pseudo-polynomial DP algorithm is developed and a FPTAS is derived from it by using a state–space trimming technique. In addition, the authors prove that the double unavailable interval case in NP-hard and no polynomial time algorithm can be devised unless π = ππ . Gu, Lu, Gu, and Zhang (2016) study the time-dependent aging effect with an associated processing speed (π£(π‘)) and optional maintenance (ππ) constraints applied to the total completion time optimization problem. A complexity analysis is made for makespan and, subsequently, total completion time criterion, with both being classified as NP-complete. Moreover, two DP algorithms are presented to solve the ∑ ∑ 1|π£(π‘), ππ| πΆπ problem with π(2π+1 ) and π(π2 ππ ) time complexities, respectively. ∑ Cheng, Kravchenko, and Lin (2020) analyze the 1|ππ (π π‘π )| πΆπ problem, given a ππ . The study of the complexity is evaluated and the 4.3. Completion time related criteria ∑ Lee (1996) proves that the 1|π − π| π€π πΆπ problem is NP-hard and presents a pseudo-polynomial DP algorithm to solve it based on ∑ weighted shortest processing time algorithm for 1β₯ π€π πΆπ as well as a recursive equation for the objective function. The DP is bounded by π(π(π‘1 )πmax ), where π‘1 is the start time of maintenance. Gélinas and Soumis (1997) present a thorough analysis regarding ∑ the 1|ππ | πΆπ problem by studying a DP formulation coupled with a labeling scheme and an elimination test in order to select reduced and feasible sets of solution, a complexity investigation for each step or modification in the formulation and also a pseudo-polynomial DP algorithm that can solve problems up to 100 jobs out of 200-job instances used in the experiments. Bianco, Dell’Olmo, and Giordani (1999) address the 1|ππ , ππ (πππ )| ∑ πΆπ problem with sequence dependent processing times. In order to solve this problem, the authors establish its equivalence to the Cumulative TSP and propose a DP formulation, from which two lower bounds are derived. Furthermore, two heuristics are defined and a comparative performance analysis with the bounds is done for a realistic data set, showing that heuristics are more efficient in such case. Cheng and Ding (2000) examine the complexity analysis for ∑ 1|ππ (π π‘π ), ππ | πΆπ , considering equal deteriorating rates ππ = π. Such problem is proved to be solved by a polynomial time DP algorithm of π(π5 ) complexity. 8 Expert Systems With Applications 190 (2022) 116180 E.A.G.d. Souza et al. Table 6 Completion time related problems for single machine. Authors Lee (1996) Gélinas and Soumis (1997) Bianco et al. (1999) Problem notation ∑ π€π πΆπ 1|π − π| 1|ππ | ∑ πΆπ ∑ 1|ππ , ππ (πππ )| ∑ Cheng and Ding (2000) 1|ππ (π π‘π ), ππ | 1|ππ − π, ππ (π π‘π )| Kacem et al. (2008) 1|π − π| Fan et al. (2011) ∑ 1|π − π, ππ (π‘)| πΆπ ∑ 1|π − π, ππ (π‘)| πΆπ Tanaka and Fujikuma (2012) 1|ππ | Li and Fan (2012) 1|ππ − π, ππ (π‘)| ∑ ∑ π€π πΆπ Gu et al. (2016) 1|π£(π‘), ππ| Cheng et al. (2020) 1|ππ (π π‘π )| Mor and Shapira (2020) ∑ ∑ 1| πππππ ≤ πΎ| πΆπ ∑ ∑ 1| πππππ ≤ πΎ| π€π πΆπ ∑ DP DP and Heuristics DP π(π(π‘1 − π‘0 )π‘2 ∏ (1 + ππ )) – π€π πΆπ ∑ – π(π ) πΆπ π€π πΆπ ∑ DP 5 πΆπ ∑ Method – πΆπ Ji et al. (2006) Complexity π(π(π‘1 )πmax ) πΆπ πΆπ DP and Heuristic DP, integer programming and B&B 2 2 π(π (π‘2 − π‘1 ) ) ∏ π(π2 (π‘2 − π‘1 )2 (1 + ππ )) DP DP – SSDP π(ππ‘1 ) FPTAS with DP π(2π+1 ) ∑ π(π2 ππ ) DP DP π(π3 ∑ ππ ∑ π(ππΎ) ∑ π(ππΎ ππ ) (ππ + ππ )) DP DP DP Jeng and Lin (2004) explore two optimal procedures to solve the 1|ππ (ππ , π π‘π )|πΆmax problem, where the processing times are defined as nonlinear step functions. The first approach is an π(π(max ππ + max ππ )) pseudo-polynomial DP algorithm and the second one relies on a B&B. Each procedure is modified by the inclusion of dominance rules, however, as experiments show, the procedures reach memory capacity, suggesting further research should focus on improvements. Bosio and Righini (2009) evaluate the 1|ππ (ππ , π π‘π ), ππ |πΆmax problem. A DP algorithm associated with construction of upper and lower bounds is provided and an overall analysis regarding the range of ππ and ππ and their effect upon the upper and lower bounds are described through computational experiments. Zhang et al. (2010) propose a DP formulation to solve the ∑ 1|ππ , πππππ ≤ πΎ|πΆmax problem taking into account a recursive relation that is dependent on the makespan of the accepted jobs for each stage ∑ with π(π(ππ + ππ )) complexity. The problem is categorized as NP-hard, due to the complexity analysis performed on the problem without the release dates. Davari, Ranjbar, De Causmaecker, and Leus (2020) address the 1|ππ , πππ£|πΆmax , which implies that the inventory is now bounded by a capacity constraint. The authors study the complexity and the problem is proved to be strongly NP-hard even for an infinite capacity inventory. In addition, two MIP formulations, a B&B method and a guess-andcheck DP algorithm are provided. Experiments are carried out on, at most, 50 jobs and the guess-and-check DP outperforms the other methods in terms of CPU times and number of solved problems. Mor and Shapira (2020) address a DP formulation for solving the ∑ 1|ππ , πππππ ≤ πΎ|πΆmax problem. The theoretical approach is unfolded into computational experiments that can solve instances with up to 2000 jobs and a varying set of rejection rate that can be extended to at most 40% with π(ππΎ) computational complexity. Problems in which makespan is considered the main criterion are summarized in Table 7. problem is classified as binary NP-hard. The authors also work on a pseudo-polynomial DP algorithm and show its complexity can be ∑ ∑ evaluated at π(π3 ππ (ππ + ππ )), where ππ is the ordinary processing time. Mor and Shapira (2020) investigate the use of theoretical for∑ ∑ ∑ mulations in DP in order to solve the 1| πππππ ≤ πΎ| πΆπ , 1| πππππ ∑ ≤ πΎ| π€π πΆπ problems via computational tests and the complexities ∑ associated with them are π(ππΎ) and π(ππΎ ππ ). The computational results show that excellent outcomes can be obtained for at most 2000 jobs and a varying rate of rejected jobs within a short time for the first problem and for at most 60 jobs regarding the second type of problem. Table 6 summarizes the content of this subsection. 4.4. Makespan Kunnathur and Gupta (1990) propose several approaches to deal with 1|ππ (ππ )|πΆmax problem, which are composed of two DP methods, a B&B and five heuristics. Although, from a theoretical point of view, DP is sustained by strong properties, its computational requirements were considered infeasible. Therefore, the experimental analysis was conducted from a comparison between the B&B and the best heuristic out of the five that have been provided. Kubiak and van de Velde (1998) apply theoretical and empirical approaches to solve the 1|ππ (π·π , ππ )|πΆmax , where ππ is a common due date at which jobs start deteriorating and π·π is a bounded due date at which jobs no further deteriorate. The theoretical content encloses three pseudo-polynomial DP algorithms to solve the unbounded and bounded job deteriorating cases while the empirical methodology encompasses a B&B algorithm and heuristics. The complexities of the DP algorithms are described in Table 7. Cheng and Ding (2000) prove that solving the 1|ππ (π π‘π ), ππ |πΆmax problem is equivalent to finding the optimal solution to the flow time case. Therefore, the DP approach can be applied with no modifications required. Ultimately, the DP algorithm presents itself as an alternative solution for 1|ππ (π π‘π ), ππ |πΏmax with π(π6 log π) (see Table 4) time complexity. Furthermore, with the DP theoretical approach, the authors manage to prove that both problems are NP-complete via a 3-partition problem. Woeginger (2000) studies the effect of the general transformation scheme of DP algorithms in FPTAS for the 1|ππ (π)|πΆmax problem as well. Theoretical background is extracted from Kubiak and van de Velde (1998) so as to perform the shifting procedure. 4.5. Multi-criteria and additional objective functions Van Wassenhove and Gelders (1978) propose four approaches, two ∑ of which are DP, to solve the bicriteria 1β₯ π€π ππ + ππ πΆπ problem. The authors resort to dominance rules based on precedence constraints and experimental tests are performed in a comparative manner for 25 jobs maximum. The DP algorithms outperformed the other methods for cases up to 20 jobs, however dual algorithms might be more efficient as the number of jobs increases. 9 Expert Systems With Applications 190 (2022) 116180 E.A.G.d. Souza et al. Table 7 Makespan problems for single machine. Authors Problem notation Complexity Method Kunnathur and Gupta (1990) 1|ππ (π π‘π )|πΆmax – DP, B&B and Heuristics ∑ Kubiak and van de Velde (1998) 1|ππ (ππ )|πΆmax 1|ππ (ππ , π·π )|πΆmax 1|ππ (ππ , π·π )|πΆmax π(πππ ππ ) − π(πππ ) ∑ π(π2 ππ (π·π − ππ ) ππ ) − π(πππ (π·π − ππ )) ∑ ∑ ∑ ∑ π(πππ ππ ( ππ )2 ) − π(πππ ππ ππ ) DP and B&B DP and Heuristics DP and Heuristics Cheng and Ding (2000) 1|ππ (π π‘π ), ππ |πΆmax – DP Woeginger (2000) 1|ππ (π)|πΆmax – FPTAS with DP Jeng and Lin (2004) 1|ππ (ππ , π π‘π )|πΆmax π(π(max ππ + max ππ )) DP and B&B Bosio and Righini (2009) 1|ππ (ππ , π π‘π ), ππ |πΆmax – DP ∑ πππππ ≤ πΎ|πΆmax Zhang et al. (2010) 1|ππ , Davari et al. (2020) 1|ππ , πππ£|πΆmax Mor and Shapira (2020) 1|ππ , ∑ πππππ |πΆmax π(π(ππ + ∑ ππ )) DP – Guess-and-Check DP π(ππΎ) DP Hoogeveen and van de Velde (1991) explore the complexity of ∑ ∑ 1|ππ = π| π€π |π − πΆπ | when π < ππ is imposed. The authors prove the problem is NP-hard and present a DP algorithm with time and space complexities of π(π2 π) and π(ππ), respectively. Moreover, some specific cases within this scenario are presented as polynomially solvable. Potts and Van Wassenhove (1992a) incorporate additional methods ∑ to the 1β₯ ππ problem by devising approximation algorithms derived from DP formulations and B&B. The approximation methods have been developed by aggregating rounding techniques into the DP so as to produce higher quality and less complex (in the computational sense) algorithms. Potts and Van Wassenhove (1992b) analyze properties related to ∑ the 1β₯ ππ problem as well as complexity analysis by showing it is NP-hard. Moreover, the authors develop a heuristic for setting an initial sequencing and a pseudo-polynomial DP algorithm of π(ππ π΅) complexity, which is able to yield solution up to 10000-job instances due to space–state reductions performed via optimality properties. Carraway, Chambers, Morin, and Moskowitz (1992) apply general∑ ized DP to solve the nonlinear multi-criteria 1β₯ (ππ1 π€π ππ + πππ2 π€π ππ ) problem and compare the results with a DP-based heuristic and a DP formulation to generate feasible sets. The heuristic and generalized DP show similar results and both outperform the DP formulation, since the last one may also admit sub-optimal schedules and fails rapidly due to the curse of dimensionality. The authors suggest using the technique so as to develop further studies regarding different nonlinear multi-criteria problems. De, Ghosh, and Wells (1992) devise a pseudo-polynomial DP algorithm by adding V-shaped properties to identify optimal solutions ∑ ∑ for 1β₯ (πΆπ − πΆ π ) with overall complexity of π(π2 ππ ). Experiments are carried out for at most 100 jobs and DP procedure outperforms a B&B algorithm and an enumeration method for the same time limit. Nevertheless the algorithm shows greater efficiency when processing times are small, therefore an approximation algorithm is also developed. Additionally, the DP approach is extended to the 1β₯(πΌπΆ π + (1 − πΌ)(πΆπ − πΆ π )) bi-criteria problem, using V-shaped structure to construct feasible sets that contain optimal solutions. Bard, Venkatraman, and Feo (1993) combine the generation of state spaces inherent to DP approaches with a B&B algorithm in order to ∑ reach optimality for the 1β₯ (πΌπ πΈπ + ππ πΆπ ) problem. A GRASP heuristic is also programmed so as to furnish a tight upper bound and fortify the fathoming in the B&B-DP. Optimality has been provided up to 30 jobs regardless the composition of the data in less than 12 min and with steady computational effort. Ibaraki and Nakamura (1994) apply successive sublimation DP to ∑ solve the 1β₯ (πΌπ πΈπ + π½π ππ ) problem. The procedure includes heuristics in order establish an initial upper bound and recursive lower bounds are derived from modifiers, job penalties and state–space relaxation. Barnes and Vanston (1981) present a DP method by coupling B&B features (DPBB) to solve the problem of minimizing the sum of delay penalties and setup costs. This method reduces the nodes explored in the DP states, thus reducing the effects of the curse of dimensionality inherent to a ‘‘pure’’ DP formulation. The computational experiments are performed for 10, 15 and 20-job data sets and compared with B&B and heuristics. The DPBB method has shown best performance regarding solution quality and CPU times for the 15 and 20-job sets whereas the B&B presented better outcomes for the 10-job set. Chand and Schneeberger (1988) build a modified Smith heuristic and a DP algorithm to minimize weighted earliness criterion subject to no tardy jobs. The DP algorithm operates in backward recursion and makes use of an efficient frontier, which stores optimal values of weighted earliness and tardy jobs, to schedule jobs as further stages are created. The authors acknowledged that DP was generated to serve as benchmark for studying heuristics. In fact, the proposed heuristic provides good quality solutions and better CPU times. Abdul-Razaq and Potts (1988) derive six lower bounds from a DP state–space relaxation to reduce the number of states generated by job assignments. Each bound is built upon a combination of modifiers and job penalties (similar to Lagrangian multipliers) so as to make them tighter. In addition, three B&B algorithms are implemented with less combinations than those designed for the DP formulation. Ultimately, ∑ the chosen problem to apply the methods was 1β₯ (πΌπ πΈπ + π½π ππ ) with DP being suitable for small-sized instances whereas B&B performs better for medium-sized instances with small processing times. ∑ Hall and Posner (1991) show that the 1|ππ = π| π€π |π − πΆπ | problem (π being unrestrictively late) is NP-complete in the ordinary sense and presents a DP algorithm along with four special cases of the problem, which can each be solved with polynomial time algorithms. The second portion of this article is seen in Hall, Kubiak, and Sethi ∑ (1991) and investigates 1|ππ = π| |π − πΆπ | (π placed early enough for the allocation process) by proving it to be NP-complete in the ordinary sense. A DP pseudo-polynomial algorithm is introduced and shows promising results for being able to solve up to 1000 jobs. De, Ghosh, and Wells (1991) focus on presenting properties related ∑ to V-shaped structures for 1|ππ = π| (πΌπ πΈπ + π½π ππ ) with asymmetrical weights and state that this problem is NP-complete in the strong sense. Furthermore, a DP algorithm is developed to ensure an exact approach to the problem as well as an approximation algorithm. Ultimately some particular cases are displayed. Yano and Kim (1991) evaluate the use of a DP procedure for solving ∑ optimally the 1β₯ (πΌπ πΈπ + π½π ππ ) problem, assuming the sequence of jobs is already given and focusing on timing as a decision making process. They also present theoretical and experimental B&B and heuristics formulations to solve a specific case when penalties are proportional to the jobs’ processing times. 10 Expert Systems With Applications 190 (2022) 116180 E.A.G.d. Souza et al. The method is executed for data sets up to 35 jobs and compared with an original DP formulation, obtaining superior outcomes both in CPU times and number of generated states. Chand, Chhajed, and Traub (1994) propose a DP algorithm to minimize the lead time (LT) and earliness costs considering fixed-delivery intervals (ππ , ππ ) by setting a first-come first-deliver priority rule. Reductions in the state space are provided through several dominance rules and compared to a full DP approach in an experiment containing up to 150 jobs. Results are considered better in terms of CPU times for the former approach. Liman and Ramaswamy (1994) describe properties related to restrictive and non-restrictive common due windows for the problem ∑ 1|ππ€ | (πΌπ πΈπ + π€π ππ ). In addition they show the NP-completeness for both situations and develop a DP pseudo-polynomial algorithms for ∑ each case with overall complexity π(π2 (ππ€ ) ππ ). Hariri, Potts, and Van Wassenhove (1995) bring a theoretical work ∑ on preemptive and non-preemptive 1β₯ π€π ππ by stating complexity analysis for both problems. In addition, the authors offer a DP-based B&B algorithm, in which DP, in conjunction with reduction properties, is used for designing upper and lower bounds efficiently. Instances ranging from 100 to 700 jobs show DP bounds efficiency by obtaining a small number of nodes before reaching optimal solution. Ventura and Weng (1995) improve the method proposed in Hall et al. (1991) by providing a pseudo-polynomial DP algorithm that stems from an elimination process of two subroutines in the original version. This enhances the method significantly in computational requirements ∑ and yields an π(π(π + ππ )) overall complexity. Weng and Ventura (1996b) propose a pseudo-polynomial DP al∑ gorithm and a heuristic to minimize 1|ππ = π, π‘π | (πΈπ + ππ ). Some properties involving LPT-SPT ordering are outlined and optimality is ensured by DP if ππ ≤ ππ implies π‘π ≤ π‘π . Comparative tests are performed for π = 8, 9, 10 with both methods being quite efficient and DP reaching near optimal solutions, indicating it could be used to ease the search for optimal solutions in larger job sizes. Weng and Ventura (1996a) describe properties related to the ∑ 1|ππ = π| [(πΆπ − π)2 ]βπ problem by associating optimal scheduling ∑ with V-shaped structure. Furthermore, the authors design an π(π ππ ) pseudo-polynomial DP algorithm for the tightly restrictive case, for which no strategy had yet been developed, and provide optimal solutions up to 100-job data sets in less than two seconds in CPU time. Lann and Mosheiov (1996) explore the minimization of ∑ 1β₯ (π·π + ππ ), with π·π denoting the number of early jobs, by providing algorithms for solving the job-independent and job-dependent with symmetrical and asymmetrical costs scenarios (in Table 8, ππ π¦ and π π¦ stand for asymmetrical and symmetrical costs, respectively), where DP formulations are given for the last two cases. They develop a polynomial DP algorithm of π(π2 ) time complexity for the symmetrical cost situation and a pseudo-polynomial DP method with ∑ π(π max{ ππ , πmax }) complexity, which is the basis for two heuristics used to solve the asymmetrical case. ∑ Cheng, Chen, and Li (1996) analyze the 1|ππ (π₯π )|(ππ , π₯π ) bi-criteria problem, where π₯π represents resources allocated to a given job and ππ (π₯π ) indicates controllable processing times dependent on this resources. Complexity theorems stating the NP-hardness are shown and sequencing properties based on EDD rule are given. In addition pseudopolynomial DP algorithms are provided for a linear non-decreasing function and a general non-decreasing function of π₯π . Cheng, Janiak, and Kovalyov (1998) examine several bi-criteria minimization problems with resource dependent processing times, considering a non-negative time compressing rate ππ and initial processing ∑ ∑ time ππ . The DP algorithms are applied to the 1β₯( π£π π₯π ≤ πΎ, π€π ππ ) ∑ ∑ ∑ and 1β₯( π£π π₯π , π€π ππ ≤ πΎ) problems with π(πΎππ π΅ ππ ), where ππ ≤ ππ βππ . In addition, the DP algorithms can be altered into approximation algorithms. Woeginger (2000) also applies the properties delineated by Hariri et al. (1995), Potts and Van Wassenhove (1992a) to show the develop∑ ment of a FPTAS is likely to occur when the DP formulations for 1β₯ ππ ∑ and 1β₯ π€π ππ are modified accordingly. Klamroth and Wiecek (2001) develop a DP algorithm in order to find the optimal schedule for a general multiple criteria optimization problem, whose objective functions are dependent on time and also bounded by a resource availability constraint. The authors model the problem as a multiple criteria knapsack problem and develop the DP algorithm based on previous references of DP for the related knapsack formulation. Yeung, OΔuz, and Cheng (2001a) introduce optimal properties for ∑ the 1|ππ€ | (πΌπ π·π + π½π ππ ) problem and prove the NP-completeness as∑ sociated to it. They also develop an π(π2 πmax (1 + ππ β2)) pseudopolynomial DP algorithm, which is unfolded in two types for solving problems with either presence or absence of straddling jobs. Computational tests are performed and the algorithm is limited to solving problems with 100 jobs within reasonable time. Yeung, Oguz, and Cheng (2001b) discuss optimal schedule proper∑ ties related to the multi-criteria 1|ππ€ | (πΌπ πΈπ + π½π ππ + ππ π·π + ππ ππ ) + ∑ πΏ(ππ€ ) and 1|ππ€ | (πΌπ πΈπ + π½π ππ + π€π πΆπ ) + πΏ(ππ€ ) problems bounded by a given due window. Two pseudo-polynomial DP algorithms, one for each problem, are designed with time complexity given by π(π3 (πΎ + ∑ ∑ 1)π2max ( ππ + 1)( ππ − πΎ + 1)2 ). Additional polynomially solvable cases are presented. Ventura, Kim, and Garriga (2002) aim at finding the optimal sched∑ ule as well as the release dates that minimize the 1|ππ | (π (ππ ) + πΌπ πΈπ + π½π ππ ) problem, in which π is a non-increasing function of release dates. A DP algorithm imbued with V-shaped ordering properties is conceived and heuristics are also provided. Despite small CPU times, the DP approach does not seem to be more advantageous than the heuristics since memory overreaching occurs for instances larger than 40 jobs while heuristics achieve high quality solutions by demanding less computational effort. Hendel and Sourd (2005) apply the DP concepts to generate a ∑ formulation to solve the 1β₯ (πΈπ + ππ ). Despite being the main element for a pairwise interchange approach, the DP formulation, which is of π(π2 ) complexity, is seen as an auxiliary method that can be coupled within a neighborhood search algorithm to finally solve the problem. Kedad-Sidhoum, Solis, and Sourd (2008) evaluate the performance of several lower bounds and a DP-based heuristic to solve the ∑ 1β₯ (πΈπ + ππ ). The π(π2 ) polynomial DP formulation is included in the process in order to reduce the memory usage when storing previous information regarding the heuristic solutions. ∑ Tanaka et al. (2009) investigate the 1|ππ − ππππ| ππ (πΆπ ) problem. A series of theorems are outlined and applied in order to reduce the computational space requirements to store the DP states in the successive sublimation DP algorithm proposed to solve the scheduling problem. These modifications lead to an efficient algorithm with capacity to optimally solve up to 300 jobs within reasonable time. Cheng and Sun (2009) develop several DP algorithms and FPTAS for ∑ ∑ ∑ the 1|ππ (π π‘π ), ππ , πππ| π€π πΆπ + πππππ , 1|ππ (π π‘π ), ππ , πππ|πΆmax + πππππ and ∑ πππ 1|ππ (π π‘π ), ππ , πππ|(πmax βπΏmax ) + ππ problems. A detailed assessment of each algorithm’s complexity is given (see Table 8) and an π(π2 ) DP al∑ gorithm is provided for 1|ππ (π π‘π ), ππ , πππ|πΆmax + πππππ with deteriorating rates ππ = π. Zhang, Lu, and Yuan (2009) analyze the complexity formulations ∑ the 1|πππ, ππ |πΆmax + πππππ and categorize the problem as NP-hard. In addition, the authors provide polynomial and pseudo-polynomial DP algorithms as well as approximation schemes (see Table 8) for the general problem and specific cases. Zhao and Tang (2011) supplement the work done in Fan et al. (2011) by extending the completion time model to two other optimiza∑ ∑ tion problems: 1|β(π), π − π, ππ (π‘)|πΌ πΆπ + π½ ππ and 1|β(π), π − π, ππ (π‘)| ∑ ∑ πΌ πΆπ + π½ πΈπ . Each problem is solved from a DP perspective and 11 Expert Systems With Applications 190 (2022) 116180 E.A.G.d. Souza et al. Li and Yuan (2020) focus on a variety of problems related to a multiagent scheduling with the intent of minimizing the total weighted late work criterion. They introduce some notations in order to separate the various forms of minimization, classify some problems regarding their complexity and develop an exact pseudo-polynomial DP algorithm with ∏ π(π2 π π΅π₯ ) and an approximation method for a specific case in which Pareto-optimal solutions are sought with a fixed number π₯ of agents. Mosheiov and Oron (2021) develop a pseudo-polynomial DP al∑ gorithm in order to solve the 1|π ππ΄| ππ , where RMA denotes a rate modifying activity associated with a maintenance the machine undergoes, which means that the processing time is subject to a reduction after the maintenance process, for a given time interval π . The algorithm is based on cases in which EDD, RMA and delayed jobs are taken into account. For each case, an appropriate recursive relation is formulated and the sequence is obtained in a backward manner. ∑ In the end, the algorithm’s complexity is estimated at π(π( ππ + π )). Computational experiments are performed for instances with up to 200 jobs and DP proves to be efficient in solving them. the authors examine the complexity of the algorithms and classify both problems as NP-hard. Tanaka and Fujikuma (2012) extend the successive sublimation al∑ gorithm DP for the following two cases: 1β₯ (πΌπ πΈπ + π½π ππ ) and ∑ 1|ππ | (πΌπ πΈπ + π½π ππ ). The SSDP has been able to find optimal solution for instances with up to 200 jobs. Tanaka and Sato (2013) also apply the successive sublimation al∑ gorithm to the 1|ππ − ππππ, ππππ| (πΌπ πΈπ + π½π ππ ) problem and the results are quite promising, given that solution has been found for all instances in the 50-job data set. Yin, Liu, Cheng, Wu, and Cheng (2013) bring a contemporary approach to a class of problems that include common due date as an endogenous element in the decision making process, considering positional learning effect and past sequence-dependent delivery times (psd). Four different objective functions are considered and also some specific cases are outlined. An π(π3 ) time complexity DP algorithm is ∑ ∑ developed to minimize the 1|πΏπ, πππ π |πΌ πΈπ + π€π ππ + πΎπ. Moreover, another π(π3 ) time complexity DP approach is offered as solution to the ∑ ∑ 1|πΏπ, πππ π |πΎ π + π€π problem. Zhao, Hsu, Cheng, Yin, and Wu (2014) evaluate solutions to min∑ imize the 1|ππ (π π‘π )| π€π ππ + πΎπ, where π is also to be determined by the optimization process. The authors prove the problem is NP-hard and ∑ design two pseudo-polynomial DP algorithms, which possess π(π π€π ) ∏ and π(ππ (1 + ππ )) complexities, and an approximation scheme to deal with the optimization. Xingong and Yong (2015) analyze two problems with positional learning effect, which main objective is to minimize πΉ (π, π) = π(π) + ∑ ∑ πΌ πΈπ + π½π , where π(π) is a variable that represents the assigned due dates and π½π denotes a penalty associated with a discarded job. Common (CON) and slack due date (SLK) rules are applied for the due date assignment. π(π4 ) and π(π3 ) polynomial time DP algorithms are employed as solution methods for each problem, respectively. Ben-Yehoshua and Mosheiov (2016) investigate the complexity be∑ havior related to the 1β₯ ππ problem, where ππ represents the early work criteria, and present proofs for its NP-hardness in the ordinary ∑ sense. Furthermore, a pseudo-polynomial DP algorithm with π(π ππ ) complexity is proposed and its results show that it can solve instances with up to 200 jobs efficiently. ∑ Yin, Xu et al. (2016) study the 1|ππ| ππ problem, given that a fixed interval (π‘1 , π‘2 ) is defined for the maintenance to occur. The authors propose two pseudo-polynomial DP algorithms, whose complexities are given by π(ππ‘1 (π‘1 +π )) and π(ππ (π‘1 +π )) (with π being a threshold), respectively. Additionally, a FPTAS is also provided and experiments are performed on each algorithm. The second DP algorithm outperforms the first in terms of CPU time and optimal solutions have been found for at most 45 jobs for either. The FPTAS reduces the state space generated by the DP algorithms and is able to find solution with up to 85 jobs depending on the approximation parameter. Wang, Kang, Shiau, Wu, and Hsu (2017) address the two-agent ∑ problem denoted by 1β₯ ππ βΆ πΏmax ≤ πΎ. The article focuses on exploring exact methods, which are comprised of two pseudo-polynomial DP algorithms and a B&B, and a Tabu Search (TS) in order to analyze their performances. Although the DP approaches for this problem are deemed fairly good methods, their practical usage is limited to smallsized instances and therefore, the comparison is estimated for the B&B and TS. For the complexity description seen in Table 8 we consider two ∑ ∑ parameters, which are ππ = ( ππ )π΄ + ( ππ )π΅ and π π = max{(ππ )π΄ + (ππ )π΄ − 1}. Bülbül, Kedad-Sidhoum, and Εen (2019) analyze solvability for the ∑ ∑ following problems 1|β(π), π − π| (πΈπ + ππ ), 1|β(π), π π − π| (πΈπ + ππ ) ∑ and 1|β(π), ππ − π| (πΈπ + ππ ). The authors prove that the nonresumable and semi-resumable cases about a common non-restrictive common due date is NP-hard in the strong sense and for special cases involving the three scenarios, in which the problem is NP-hard in the ordinary sense, pseudo-polynomial DP algorithms are developed for optimal scheduling. 4.6. Discussion on single machine problems One of the enriching discussions of this environment is that DP enabled the development and application of several approaches, and as one can notice, no pattern has been dominant over the years. This feature is a confirmation that the single machine environment has a large potential in the innovation field in machine scheduling due to a variety of theoretical and practical background it has to offer. For starters, we can cite the paper developed by Lawler and Moore (1969), which correlates the single machine environment with the knapsack problem for a handful of objective functions. As a result of that, the DP formalism applied to the knapsack problem was, with proper ∑ ∑ ∑ modifications, used as a resource to model π€π πΈπ , ππ , π€π ππ and ∑ ππ functions and minimize them via recursion. Baker (1977) and Lawler (1977) have also shown relevant contribution to the machine scheduling environment for tardiness-related functions by developing decomposition properties and labeling scheme, respectively so as to reduce the state space associated with the storage of DP recursive methods. Potts and Van Wassenhove (1982) have made use of both approaches and combined them, being able to reach practical results for 70 jobs with a polynomial time complexity algorithm. At a posterior work (Potts & Van Wassenhove, 1987), they adapt a series of algorithms by including decomposition and precedence properties and prove that decomposition algorithms outperform the precedence ones by reaching optimal solution for 100 jobs at most within reasonable ∑ time for ππ function. Ultimately, this can be seen as a remarkable work because it was a leap for DP algorithms due to the Curse of Dimensionality in terms of efficiency relating core storage and CPU time. Authors have also been concerned with combining DP with other methods to either reinforce the DP efficiency by reducing its state space or to generate a more powerful algorithm on the other end. This can be observed in Potts and Van Wassenhove (1988) to minimize ∑ π€π ππ by designing lower bounds from the knapsack-like DP approach seen in Lawler and Moore (1969) and a combination of B&B and DP that are improved with reduction theorems and can solve problems as large as 1000 jobs. Hariri and Potts (1994) also aim at minimizing the weighted version of the same function with deadlines by using DP as a subroutine for job penalties, showing promising results for at most 300 jobs. Additionally, the organization and theorems proposed by Woeginger (2000) has enabled the existence of several FPTAS that depend on DP not only in single machine scheduling but also in other environments, as we will mention later. SSDP is one of the modified structures of pure DP that has also appeared recurrently and is usually introduced in Tanaka’s papers to solve tardiness related problems (Tanaka & Fujikuma, 2012; Tanaka & Sato, 2013) and makespan problems (Tanaka & Fujikuma, 2012). 12 Expert Systems With Applications 190 (2022) 116180 E.A.G.d. Souza et al. Table 8 Multicriteria and additional functions problems for single machine. Authors Van Wassenhove and Gelders (1978) Barnes and Vanston (1981) Chand and Schneeberger (1988) Abdul-Razaq and Potts (1988) Hall and Posner (1991) Hall et al. (1991) De et al. (1991) Yano and Kim (1991) Hoogeveen and van de Velde (1991) Potts and Van Wassenhove (1992b) Potts and Van Wassenhove (1992a) Carraway et al. (1992) De et al. (1992) Bard et al. (1993) Ibaraki and Nakamura (1994) Chand et al. (1994) Liman and Ramaswamy (1994) Hariri et al. (1995) Ventura and Weng (1995) Weng and Ventura (1996b) Weng and Ventura (1996a) Lann and Mosheiov (1996) Cheng et al. (1996) Cheng et al. (1998) Woeginger (2000) Klamroth and Wiecek (2001) Yeung et al. (2001a) Yeung et al. (2001b) Ventura et al. (2002) Hendel and Sourd (2005) Kedad-Sidhoum et al. (2008) Tanaka et al. (2009) Cheng and Sun (2009) Zhang et al. (2009) Zhao and Tang (2011) Tanaka and Fujikuma (2012) Tanaka and Sato (2013) Yin et al. (2013) Zhao et al. (2014) Xingong and Yong (2015) Ben-Yehoshua and Mosheiov (2016) Yin, Xu et al. (2016) Wang et al. (2017) Bülbül et al. (2019) Li and Yuan (2020) Mosheiov and Oron (2021) Problem notation ∑ 1β₯ π€π ππ + ππ πΆπ ∑ 1β₯ πΉ (π ππ ) + πΊ(π€π ππ ) ∑ ∑ 1β₯( π€π πΈπ , ππ = 0) ∑ 1β₯ (πΌπ πΈπ + π½π ππ ) ∑ 1|ππ = π| π€π |π − πΆπ | ∑ 1|ππ = π| |π − πΆπ | ∑ 1|ππ = π| (πΌπ πΈπ + π½π ππ ) ∑ 1β₯ (πΌπ πΈπ + π½π ππ ) ∑ 1|ππ = π| π€π |π − πΆπ | ∑ 1β₯ ππ ∑ 1β₯ ππ 1β₯(ππ1 π€π ππ + πππ2 π€π ππ ) ∑ 1β₯ (πΆπ − πΆ π ) 1β₯(πΌπΆ π + (1 − πΌ)(πΆπ − πΆ π )) ∑ 1β₯ (πΌπ πΈπ + ππ πΆπ ) ∑ 1β₯ (πΌπ πΈπ + π½π ππ ) ∑ 1|(ππ , ππ )| πΈπ + ππ πΏπ ∑ 1|ππ€ | (πΌπ πΈπ + π€π ππ ) ∑ 1β₯ π€π ππ ∑ 1|ππ = π| |π − πΆπ | ∑ 1|ππ = π, π‘π | (πΈπ + ππ ) ∑ 1|ππ = π| [(πΆπ − π)2 ]βπ ∑ 1β₯ (π·π + ππ ) ∑ 1β₯ (π·π π π¦ + ππ π π¦ ) ∑ 1β₯ (π·π ππ π¦ + ππ ππ π¦ ) ∑ 1|ππ (π₯π )|(ππ , π₯π ) ∑ ∑ 1β₯( π£π π₯π ≤ πΎ, π€π ππ ) ∑ ∑ 1β₯( π£π π₯π , π€π ππ ≤ πΎ) ∑ 1β₯ ππ ∑ 1β₯ π€π ππ ∑ 1β₯(ππ (π‘)), π₯π ∑ 1|ππ€ | (πΌπ π·π + π½π ππ ) ∑ 1|ππ€ | (πΌπ πΈπ + π½π ππ + ππ π·π + ππ ππ ) + πΏ(ππ€ ) ∑ 1|ππ€ | (πΌπ πΈπ + π½π ππ + π€π πΆπ ) + πΏ(ππ€ ) ∑ 1|ππ | (π (ππ ) + πΌπ πΈπ + π½π ππ ) ∑ 1β₯ (πΈπ + ππ ) ∑ 1β₯ (πΈπ + ππ ) ∑ 1|ππ − ππππ| ππ (πΆπ ) ∑ ∑ 1|ππ (π π‘π ), ππ , πππ| π€π πΆπ + πππππ ∑ 1|ππ (π π‘π ), ππ , πππ|πΆmax + πππππ ∑ 1|ππ (π π‘π ), ππ , πππ|(πmax βπΏmax ) + πππππ ∑ πππ 1|ππ (π π‘π ), ππ = π, ππ , πππ|πΆmax + ππ ∑ 1|πππ, ππ |πΆmax + πππππ ∑ 1|πππ, ππ |πΆmax + πππππ ∑ 1|πππ, ππ , πππππ = π πππ |πΆmax + πππππ ∑ πππ 1|πππ, ππ , ππ = π|πΆmax + ππ ∑ ∑ 1|β(π), π − π, ππ (π‘)|πΌ πΆπ + π½ ππ ∑ ∑ 1|β(π), π − π, ππ (π‘)|πΌ πΆπ + π½ πΈπ ∑ 1β₯ (πΌπ πΈπ + π½π ππ ) ∑ 1|ππ | ((πΌπ πΈπ + π½π ππ )) ∑ 1|ππ − ππππ, ππππ| (πΌπ πΈπ + π½π ππ ) ∑ ∑ 1|πΏπ, πππ π |πΌ πΈπ + π€π ππ + πΎπ ∑ ∑ 1|πΏπ, πππ π |πΎ π + π€π ∑ 1|ππ (π π‘π )| π€π ππ + πΎπ ∑ 1|ππ (π π‘π )| π€π ππ + πΎπ ∑ ∑ 1|πΏπ, ππΏπΎ|π(π) + πΌ πΈπ + π½π ∑ ∑ 1|πΏπ, πΆππ|π(π) + πΌ πΈπ + π½π ∑ 1β₯ ππ ∑ 1|ππ| ππ ∑ 1|ππ| ππ ∑ 1β₯ ππ βΆ πΏmax ≤ πΎ ∑ 1β₯ ππ βΆ πΏmax ≤ πΎ ∑ 1|β(π), π − π| (πΈπ + ππ ) ∑ 1|β(π), π π − π| (πΈπ + ππ ) ∑ 1|β(π), ππ − π| (πΈπ + ππ ) ∑ ∑ 1β₯π ( π€π ππ(1) , … , π€π ππ(π₯) ) ∑ 1|π ππ΄| ππ Guess-and-Check DP is also a derived method proposed by Davari et al. Complexity Method – – – – ∑ π(π ππ ) ∑ π(π ππ ) – – π(π2 π) - π(ππ) π(ππ π΅) – – ∑ π(π2 ππ ) – – – – ∑ π(π2 (ππ€ ) ππ ) – ∑ π(π(π + ππ )) – ∑ π(π ππ ) – π(π2 ) ∑ π(π max{ ππ , πmax }) – ∑ π(πΎππ π΅ ππ ) ∑ π(πΎππ π΅ ππ ) – – – ∑ π(π2 πmax (1 + ππ β2)) ∑ ∑ π(π3 (πΎ + 1)π2max ( ππ + 1)( ππ − πΎ + 1)2 ) ∑ ∑ π(π3 (πΎ + 1)π2max ( ππ + 1)( ππ − πΎ + 1)2 ) – π(π2 ) π(π2 ) – ∑ π(π πππππ ) ∑ π(π πππππ ) ∏ ∑ π(π (1 + ππ ) πππππ ) 2 π(π ) ∑ π(π πππππ ) ∑ π(π(πmax + ππ )) π(π2 ) π(π3 ) ∏ ∏ π(ππ‘1 ( ππ ( (1 + πππ ) − 1) + π‘2 ( (1 + πππ ) − 1))) ∏ ∏ π(ππ‘1 ( ππ ( (1 + πππ ) − 1) + π‘2 ( (1 + πππ ) − 1))) – – – π(π3 ) π(π3 ) ∑ π(π π€π ) ∏ π(ππ (1 + ππ )) π(π4 ) π(π3 ) ∑ π(π ππ ) π(ππ‘1 (π‘1 + π )) π(ππ (π‘1 + π )) ∑ π(ππ΄ ππ΅ min{(ππ , π π, ( ππ )π΅ })) ∑ π(ππ΄ ππ΅ ( ππ )π΄ ) – – – ∏ π(π2 π π΅π₯ ) ∑ π(π( ππ + π )) DP and Dual algorithm DPBB DP and Heuristic DP and B&B DP and FPTAS DP DP and Approximation algorithm DP DP DP Approximation with DP and B&B Heuristic with DP and B&B DP DP B&B with DP and Heuristic SSDP DP DP B&B with DP DP DP and Heuristic DP DP and Heuristics DP DP DP DP and Approximation algorithm DP and Approximation algorithm FPTAS with DP FPTAS with DP DP DP DP DP DP Heuristic with DP Heuristic with DP and LBs SSDP DP and FPTAS DP and FPTAS DP and FPTAS DP DP and Approximation algorithm DP and Approximation algorithm DP DP DP DP SSDP SSDP SSDP DP DP DP DP DP DP DP DP and FPTAS DP and FPTAS DP, B&B and TS DP, B&B and TS DP DP DP DP and Approximation algorithm DP Regarding completion time related criteria, one can notice that most of them are concentrated on maintenance constraints and that the majority resorts to pure DP in order to solve the various problems involving completion times with different types of constraints. The papers encompass pure DP formulations, comparisons with heuristics, integer programming and B&B and also the development of FPTAS with (2020) for the makespan analysis. Note that this last one is a recent paper and therefore, a novel method that could be a potential asset in further research involving DP, given that for the 1|ππ , πππ£|πΆmax (which is strongly NP-hard) it has outperformed a B&B method and a MIP. 13 Expert Systems With Applications 190 (2022) 116180 E.A.G.d. Souza et al. Fig. 1. Number of papers, separated by journal, that includes DP as solution method for single machine scheduling problems. Fig. 2. Frequency of DP in single machine scheduling problems per journal. DP as main subroutine. Makespan, which is analyzed separately in this section, entails majorly problems with controllable processing times, which is one of the forms that makespan becomes a function of interest in the optimization for the single machine environment. Pure DP is presented in conjunction with other methods or studied as one of the methods that could be applied in order to solve the problem. The last subsection encompasses multi-criteria and additional functions that are not considered regular according to the definition in the previous section. The main point that must be discussed regarding it is that since last decade, many objective functions have been leaning towards the use of resources constrained by a threshold, penalties on rejected jobs and multi-agent functions. The reason for that might be explained due to the fact that many of the manufacturing companies operate on shortage of resources and, while the process is ongoing, there might exist the need to prioritize some of the components in the system. The classic objective functions in literature, despite being crucial for the development of scheduling, may often incorporate assumptions that could be unrealistic in the industrial scenario. Therefore, many authors have been more interested in investigating situations that might appear more frequently in the shop floor. Despite all the papers that have been produced over these years with respect to single machine scheduling there are some gaps that can be pointed out in literature. The first one is related to the tardinessrelated criteria and according to our research, precedence constraints and unconstrained are often investigated using DP as solution method. Therefore, problems considering other constraints such as release dates, common due dates, preemption, among others should be looked at. Even though the Curse of Dimensionality may represent a major drawback, with new methods derived from DP, its effects can be mitigated when including such constraints. This also leads to the second point that should be the formulation of new dominance rules, labeling schemes and decomposition properties in order to reduce the state space. By doing so, the storage problems are also diminished and the efficiency of DP can also be improved. In addition, SSDP, proposed in Tanaka’s papers, has shown promising results for several classic objective functions and it may indicate that it is a strong candidate to be applied to other models involving makespan, earliness and tardiness and also problems that entail the more recent functions (e.g. job rejection). Lastly, one can notice that a large portion of the articles focuses on the mathematical development of formulations and complexity 14 Expert Systems With Applications 190 (2022) 116180 E.A.G.d. Souza et al. Table 9 Due date related problems for parallel machines. Authors Lawler and Moore (1969) Baptiste (2000) Hall, Lesaoana, and Potts (2001) Lopes and de Carvalho (2007) Tuong et al. (2010) Pessoa, Uchoa, De Aragão, and Rodrigues (2010) Yoo and Lee (2016) Tadumadze, Emde, and Diefenbach (2020) Problem notation ∑ π πβ₯ π€π πΈπ ∑ ππβ₯ π€π πΈπ ∑ π π|π, π| ππ ∑ ππ|π, π| ππ ∑ π π|ππ = π| π€π ππ ∑ ππ|ππ = π| π€π ππ ∑ π π|ππ = π, ππ | ππ π π|ππ |πΏmax π π|ππ |πΏmax ∑ π π|ππ , π = π | ππ ∑ π π|ππ , π = π | π€π ππ ∑ π π|π πππ , ππ , ππ | π€π ππ ∑ π π|ππ = π| π€π ππ ∑ ππ|ππ = π| π€π ππ ∑ π πβ₯ π€π ππ π π|πππ|πΏmax ∑ π π|πππ| πΏπ π π|πππ|πΏmax ∑ π π|πππ| πΏπ π π|πππ, ππ = π|πΏmax ∑ π π|πππ, ππ = π| πΏπ π π|ππ , π π |π€π πΏmax analysis rather than computational experiments. Logically, it is relevant to demonstrate the former, however showing the computational performance might be as important as the mathematical analysis so as to understand the limitations a given model can present and also to encourage new researchers to tackle these challenges. The last analysis that we have made regarding the information we could extract is a qualitative analysis concerning the journals that have published the articles in which DP has been presented as solution method for single machine scheduling problems. From Fig. 1, the journal that has presented the most prominent contribution is the European Journal of Operational Research, which is accountable for 22.6% of the amount of papers that have been gathered in this research, as it is shown in Fig. 2. Other journals have also contributed significantly in publishing the DP-related articles in the single machine environment, as it can be seen by the percentages attributed to them (Operations Research, Computers and Operations Research (8.3% each), Operations Research Letters (7.1%) and Journal of Scheduling (6%)). Note that when comparing Figs. 1 and 2 more journals have been categorized in the first one. This can be explained due to the fact that the first picture considers all papers involved in our research and the second one only those that have been the most recurrent in publishing DP in single machine problems. Those that have shown less than 2% of contribution were placed in the ‘‘Others’’ category. Complexity Method – – – – – – π(π2π+2 ) ∑ π(π( ππ )π−1 ) ∑ π(π( ππ )ππ −1 ) ∑ π(π( ππ )ππ −1 ) ∑ π(π( ππ )ππ −1 ) – ∑ π(ππ+1 π 2π ( ππ )π−1 ) ∑ π(πππ+1 π 2π ( ππ )π−1 ) – π(ππ(π 1 + π 2 )π ) π(ππ(π 1 + π 2 )π ) π(πππ π3 π π4 π π ) π(πππ π3 π π4 π π ) π((π + 1)3π ) π((π + 1)3π ) – DP DP DP DP DP DP DP and Decomposition algorithm DP DP DP DP B&P with DP DP DP BCP with DP DP DP DP DP DP DP MIP, BB&C with BDP and Heuristics formulation is derived from it. Due to that, it is possible to develop ∑ a polynomial solution of π(π2π+2 ) complexity for π π|ππ = π, ππ | ππ . Hall et al. (2001) explore a series of problems concerning fixed delivery dates, which will be denoted as ππ with π indicating the number of fixed deliveries. The authors formulate two DP algorithms with ∑ ∑ π(π( ππ )π−1 ) and π(π( ππ )ππ −1 ) complexities that provide optimal solutions for the π π|ππ |πΏmax and one of them is able to yield optimal ∑ ∑ solution for the π π|ππ , π = π | ππ and π π|ππ , π = π | π€π ππ . Lopes and de Carvalho (2007) analyze a branch-and-price (B&P) ∑ algorithm to minimize π π|π πππ , ππ , ππ | π€π ππ . Due to the problem’s robustness, the algorithm relies on a series of improvements and one of those is directed to the DP formulations that compose the pricing algorithm embedded in the B&P, which is named primal box. The method is applied in instances with up to 150 jobs and 50 machines and promising results are attained. Tuong et al. (2010) extend their single-machine DP formulation to the identical and uniform machines under modifications. The assumptions of their DP are based on the existence of straddling jobs and WSPT priority rule for the fully tardy jobs. These properties generate two algorithms, each designated to its associated problem, with ∑ ∑ π(ππ+1 π 2π ( ππ )π−1 ) and π(πππ+1 π 2π ( ππ )). Pessoa et al. (2010) present a Branch-Cut-and-Price (BCP) algorithm ∑ in order to solve the π πβ₯ π€π ππ . This algorithm relies on a forward and backward DP recursion to fix variables related to Lagrangian bounds that optimize the pricing algorithm, which is one of the essential elements in the internal structure of the BCP. Experiments are placed for at most 100 jobs and 4 machines and results are promising for the scenario with the authors emphasizing the need of sophisticated methods to large-sized arc-time indexed problems such as the one presented. Yoo and Lee (2016) investigate a series of problems concerning the dependent and independent cases of maintenance on parallel machines. ∑ Their analysis include classification of π π|πππ|πΏmax , π π|πππ| πΏπ , ∑ π π|πππ|πΏmax and π π|πππ| πΏπ as NP-hard in the strong sense and DP formulations are proposed in order to solve them. Their complexities are functions of some elements relative to the maintenance activity ∑ and those are defined as π 1 = min{π − (π‘2 − π‘1 ), ( ππ + (π + 1)(π‘2 − ∑ π‘1 ) − πmax )βπ + πmax }, π 2 = ( ππ − πmax )βπ + (π‘2 − π‘1 ) + πmax , π 3 = ∑ min{π − (π − π + 1), ( ππ + (π − 1)(π‘2 − π‘1 ) + (π − 2)πmax )βπ + πmax } and ∑ π 4 = ( ππ + (π − 1)πmax )βπ + (π‘2 − π‘1 ) + πmax . Furthermore, the authors extend the DP approaches for problems with identical processing times for all the jobs. Detailed information about their complexities is shown in Table 9. 5. Parallel machines Dynamic Programming has also contributed for an extensive list of solutions regarding the parallel machine environment. Several mathematical properties have been developed for this multi-machine scenario and this fact has enabled sole or combined methods relying on dynamic programming resources to be designed. 5.1. Classic due date related criteria Lawler and Moore (1969) extend the functional DP formulation for the same problems studied in the single machine environment to parallel machines. Since loss functions are part of the formulation, they might be equal or not. This feature, combined to the behavior of processing times, generates solutions for identical and uniform machines. Baptiste (2000) proves that, since pairwise monotonicity and nondecreasing behavior can be observed for some classes of functions in scheduling, a decomposition algorithm can be applied and a DP 15 Expert Systems With Applications 190 (2022) 116180 E.A.G.d. Souza et al. Table 10 Number of tardy jobs related problems for parallel machines. Authors Lawler and Moore (1969) Li (1995) Chen and Powell (1999b) Hall et al. (2001) Chen and Powell (2003) Problem notation ∑ π πβ₯ ππ ∑ ππβ₯ ππ ∑ π πβ₯ ππ ∑ π πβ₯ π€π ππ ∑ ππβ₯ π€π ππ ∑ π πβ₯ π€π ππ ∑ π π|ππ | ππ ∑ π π|ππ | π€π ππ ∑ π π|ππΌπ | π€π ππ ∑ π π|ππ·π | π€π ππ Tadumadze et al. (2020) develop a MIP, a Benders-andCut algorithm and a heuristic in order to solve the π π|ππ , π π |π€π πΏmax . The second algorithm is in fact a decomposition of two problems, which are the master problem and the slave problem. The second one is solved by using a Bounded Dynamic Programming (BDP) approach, which is a branched method from DP that includes lower bounds and dominance rules. The authors state that the Benders-and-Cut algorithm is able to outperform the other methods for instances with up to 60 jobs and 13 machines. Complexity Method – – – ∑ π(π2 πππ ) ∑ π(π2 πππ ) ∑ π(π2 πππ ) ∑ π(π( ππ )π ) ∑ π(π( ππ )π ) 2 π(π max{π‘2 π − π‘2 π + 1}) π(π2 max{π‘2 π − π‘2 π + 1}) DP DP DP and Heuristic B&B with DP B&B with DP B&B with DP DP DP DP DP Dessouky, Lageweg, Lenstra, and van de Velde (1990) present algorithms of different types to solve several problems in uniform machines. Among those, a DP formulation is designed to compute recursively the ∑ completion times in the ππ|ππ , πππ = 1| πΆπ problem. The algorithm is bounded by an π(ππ2π+1 ) time complexity. ∑ Lee and Liman (1993) prove that the π 2|π2 ≤ πΎ| πΆπ problem is NP-complete, where πΎ represents a capacity constraint imposed on the second machine, and develop a pseudo-polynomial DP algorithm to compute the completion time recursively at each stage and a heuristic, which is proven to have a 50% error bound assuming a worst-case scenario. ∑ Alidaee (1993) establishes similarity patterns between π 2β₯ π€π πΉπ and the single machine problem investigated by Hall and Posner (1991). The author incorporates properties previously known such as V-shaped structure and proposes an adapted DP formulation with ∑ π(π π€π ) complexity for solving the identical parallel machines problem. Webster (1994) describes the DP formulation proposed by Alidaee (1993) as a specific case of the one proposed by Rothkopf (1966) for an arbitrary number of machines and a more general function, in which discounts and dependencies between jobs might be allowed. Cheng and Diamond (1995) study the problem for minimizing the ∑ π π|π½π | πΆπ , where π½π denotes job families and no job in the second family is allowed to precede jobs in the first one. The authors investigate a two-job family case and a general DP recursive formulation with π(π2 π) overall complexity is devised by adding the contribution of each scheduled job in a family to the objective function separately. Lee (1996) addresses two problems involving unavailability for the ∑ ∑ second machine on π 2|π − π| π€π πΆπ and π 2|ππ − π| π€π πΆπ . Initially, a re-indexation of jobs is made through the WSPT priority rule and a DP formulation is provided to compute the objective function in each case, ∑ ∑ yielding π(π πππ π 2 πmax ) and π(π πππ π 2 ) complexities. Alon, Azar, Woeginger, and Yadid (1998) present an ILP and a DP approach as alternative methods to constitute the formulation of ∑ a PTAS to solve the π πβ₯ π (πΆπ ). Although the DP formulation is estimated by a pseudo-polynomial bound, the ILP displays more effective results by producing a polynomial time complexity. van Den Akker, Hoogeveen, and van de Velde (1999) describe a pricing algorithm as a forward DP formulation to solve a column generation approach to a linear programming relaxation. A B&B algorithm is also provided and the authors prove that, when combined with the linear programming relaxation, it outperforms the previous algorithms ∑ used for solving π πβ₯ π€π πΆπ regarding number of jobs and CPU time. Chen and Powell (1999b) devise DP formulations, which are modifications from those used for solving the weighted number of tardy jobs, to minimize the weighted completion time for the same environments. These formulations solve each single machine sub-problem with the ∑ same π(π2 πππ ) complexity. Baptiste (2000) also verifies that the premises to apply the decom∑ position algorithm hold for the π π|ππ = π, ππ | π€π πΆπ problem. Since the algorithm has no modification from the total tardiness version, the complexity is also computed at π(π2π+2 ) bound. Lee and Chen (2000) analyze the NP-hardness related to the ∑ ∑ π π|ππ − π, πππ| π€π πΆπ and π π|ππ − π, πππ| π€π πΆπ problem, where πππ 5.2. Number of tardy jobs Lawler and Moore (1969) also extend the properties of the functional DP formulation for uniform and identical machines. Despite being presented as a natural extension this analysis performs calculations with exponential growth even for cases where machines are identical. ∑ Li (1995) proposes a heuristic method as solution for the π πβ₯ ππ , considering agreeable due dates in the process and in order to compare its results, the author develops a bounding scheme derived from a DP formulation. The experiments are applied in job sets from 50 to 200 jobs and machine sets from 2 to 5 machines. Chen and Powell (1999b) explore a branch and bound algorithm by deriving bounds from a decomposition method in order to solve ∑ ∑ ∑ the π πβ₯ π€π ππ , ππβ₯ π€π ππ and π πβ₯ π€π ππ . This decomposition method is solved by a column generation algorithm which, in turn, is subdivided into two single machine sub-problems, being each solved ∑ by a DP formulation with π(π2 πππ ) complexity. Hall et al. (2001) investigate the application of the DP formulations ∑ ∑ on π π|ππ | ππ and π π|ππ , π = π | π€π ππ with complexity bounded by ∑ π π(π( ππ ) ). Chen and Powell (2003) resort to a B&B method to solve the ∑ ∑ π π|ππΌπ | π€π ππ and π π|ππ·π | π€π ππ when a given time window (π‘1π , π‘2π ) is considered. The branching process is partitioned via decomposition and column generation algorithms until the π-machine problem can be converted into single machines sub-problems, which are solved by a DP recursion of π(π2 max{π‘2π − π‘2π + 1}) complexity (see Table 10). 5.3. Completion time related criteria Baker and Merten (1973) report a variety of results concerning the mean weighted flow time minimization, which are divided in practical and theoretical approaches. The latter states, among a series of findings, that the DP formulation proposed by Held and Karp can be used to reduce the state space for optimal solution in identical and uniform machines, however it is only fit for small and medium sized sets. Horowitz and Sahni (1976) provide algorithms to solve the ∑ π2β₯ π€π πΉπ problem and, among those, a DP algorithm is presented. Such algorithm is used to determine the partition that produces the optimal value for the objective function and subsequently, it is extended to the π-machine case with π(min{ππ π΅, 2π }) complexity. Approximation algorithms are also presented as solution methods. 16 Expert Systems With Applications 190 (2022) 116180 E.A.G.d. Souza et al. and πππ define dependent and independent availability, respectively. A column generation method is also proposed in order to provide optimal solutions for these problems working similarly to that seen in Chen and Powell (1999b). The inbuilt DP formulations are defined with π(π2 π 2 ) and π(π2 π 3 + ππ 4 π‘2 ) for the independent and dependent case, ∑ respectively. In this notation π 2 = [ ππ − πmax ]βπ + (π‘2 − π‘1 ) + πmax , ∑ ∑ π 3 = [ ππ + (π − 1)(π‘2 − π‘1 ) + (π − 2)πmax ]βπ + πmax and π 4 = [ ππ + (π − 1)πmax ]βπ + (π‘2 − π‘1 ) + πmax . Moreover, computational experiments are performed in order to test the algorithm’s efficiency for medium sized jobs (up to 60) and π ranging from 2 to 8 machines. Webster and Azizoglu (2001) propose a forward and a backward ∑ DP algorithm to solve the π π|ππΌπ | π€π πΆπ problem, where ππΌπ denotes family independent setup times. The problem is classified as NP-hard and the algorithms are pseudo-polynomial with π(ππ π+1−π ππ ∑ ∑ ( π€ )π−1 ) complexity for the backward DP and π(ππ π+2−π ππ ( π€π + ∑ ππ ππ ) ) complexity for the forward DP. Hall et al. (2001) also present the DP algorithms in the last two ∑ sections to furnish optimal solutions for the π π|ππ | πΆπ , π π|ππ , π = π | ∑ ∑ πΆπ and π π|ππ , π = π | π€π πΆπ . The algorithm used to solve the first ∑ problem produces an optimal schedule within a π(π( ππ )π−1 ) complexity while the other one, which solves the remaining problems, shows ∑ an π(π( ππ )ππ −1 ) complexity. Chen and Powell (2003) use a network-like structure for π π ∑ ∑ |ππΌπ | π€π πΆπ and π π|ππ·π | π€π πΆπ problems in association with decomposition and column generation algorithms, reaching singlemachine sub-problems, which are solved by a DP formulation bounded by π(π2 max{π‘2π − π‘1π + 1}) complexity. Ramachandra and Elmaghraby (2006) offer a BIP method and a ∑ DP algorithm to find optimal solutions for π 2|ππππ| π€π πΆπ . The DP presents better results for a larger number of jobs and processing times range, even though the DP can generate a smaller number of solutions for reduced number of jobs and processing times. A genetic algorithm (GA) is also proposed for larger number of jobs and the 2 and 3-machine cases and experimental results are registered. Mellouli, Sadfi, Chu, and Kacem (2009) evaluate the performance of ∑ exact algorithms based on MILP, B&B and DP for the π π|β(ππ )| πΆπ . Experiments are performed on job sets with up to 200 jobs and machine sets ranging from 2 to 4 machines. DP shows the best results for π = 2, being able to solve 200-job instances and reasonable results for π ≥ 2, however, for this case, its efficiency is compromised as jobs as job sets become higher than 25. Kim, Sung, and Lee (2009) investigate the minimization of ∑ π π|π − ππππ| πΆπ , where π − ππππ indicates that π precedence relationships are allowed into the scenario. The authors propose a LP∑ based heuristic, whose core solution is given by an π(π ππ ) pseudopolynomial DP approach to a separation problem. Experiments are performed for at most 300 jobs and 10 machines and the heuristic is compared to a SPT-based heuristic, proving the former obtains better results in terms of (πβπ) ratio and CPU times. Zhao, Tang, and Cheng (2009) investigate a special case of maintenance, which is the rate-modifying (denoted by πΌπ ) activity, for two ∑ identical parallel machines and π€π πΆπ criterion. The authors also develop a DP algorithm for cases where jobs are agreeable accord∑ ing to the WSPT-ratio and πΌπ -WSPT-ratio and it presents π(π( max 6 {ππ , πΌπ ππ }) ) complexity and show that the approach can be extended ∑ to a π-machine scenario with π(π( max{ππ , πΌπ ππ })3π ). Tang and Zhang (2011) devise a Lagrangian relaxation algorithm ∑ in order to minimize the π π|ππ | πΆπ problem. Such algorithm can be divided in two parts, which are connected. A relaxation decomposition is performed and it originates machine-level sub-problems, whose solvability is given by a combination of a forward DP recursion and WSPT priority rule. Experiments are performed in order to verify the efficiency of the method and it furnishes high quality solutions in reasonable CPU time for instances with up to 100 jobs and 10 machines. Zhao and Tang (2014) develop a DP approach for the ∑ π π|ππ − π, ππ (π π‘π )| π€π πΆπ problem. This algorithm utilizes the premises of the Principle of Optimality and indexation of jobs follows the weighted shortest deteriorating rate (WSDR) priority rule with com∏ ∏ ∏ plexity bounded by π(π (π‘1π − π‘0 ) (π‘2π ( 1 + ππ )π ). ∑ Yoo and Lee (2016) also derive DP algorithms for the π π|πππ| πΆπ , ∑ π π|πππ| π€π πΆπ problems, their dependent cases counterparts and the dependent cases with equal processing times for all jobs and their complexities are equivalent to those shown for the total lateness and maximum lateness. Tadumadze et al. (2020) analyze the π π|ππ , π π |π€π πΉmax problem via the same methods used for the π€π πΏmax counterpart. The results also indicate that the BB&C algorithm outperforms the other ones tested for small and medium-sized instances with up to 60 jobs and 13 machines, however the heuristic works more efficiently when problems with 100 jobs and 25 machines are considered (see Table 11). 5.4. Makespan Horowitz and Sahni (1976) also investigate solution methods to minimize makespan in parallel machines. In order to do so, a DP algorithm is devised for the π 2β₯πΆmax problem, in which the optimal schedule can be found using an SPT rule and the partition of jobs can be determined through the DP. This algorithm presents ∑ π(min{π min{ πΆππ }, 2π }) complexity and, can be naturally extended for ∑ the ππβ₯πΆmax problem with π(min{π min{ πΆππ }, ππ }) complexity. Jansen and Porkolab (2001) develop an approximation algorithm to solve the π πβ₯πΆmax problem. This method contains several steps and among them, a DP algorithm is devised in order to find an optimal schedule for jobs with long processing times, which are grouped according similarities tested against a given criterion. Such algorithm is bound with π(ππ(ππβπΏ)π ), with π being the number of jobs grouped accordingly and πΏ a partition parameter. Hall et al. (2001) applies their DP algorithms to in order to analyze the behavior for makespan. Both of them are suitable for such ∑ criterion and the complexities associated are also π(π( ππ )π−1 ) and ∑ ππ −1 π(π( ππ ) ). Ghirardi and Potts (2005) propose a beam search algorithm to solve the π πβ₯πΆmax problem. Such algorithm presents similarities to a B&B algorithm, however a DP-based pruning criterion is used in order to select which vertices should compose the solution. The theoretical results are computationally tested and compared to an approximation algorithm for jobs ranging from 100 to 1000 and machines ranging from 10 to 100. Results show that for a majority of cases the beam search shows superior results in terms of CPU times and solution quality. Tang and Luo (2006) develop a powerful iterated local search (ILS) algorithm for solving instances with up to 1000 and 40 machines regarding the π πβ₯πΆmax problem. An approximately DP algorithm is integrated to its constitution to furnish the minimum cost to a cyclic exchange in an associated graph so as to design an initial solution for the algorithm. Glass and Kellerer (2007) consider a job assignment restriction for the π 2β₯πΆmax , which means that there might occur impositions on which machines jobs are allocated to. They propose a FPTAS and an π(ππmax ) complexity DP formulation to tackle the problem, with the latter being a knapsack adapted formulation through a Subset Sum Problem analysis. Kellerer and Strusevich (2008) evaluate solutions to solve the job assignment restriction problem denoted by π 2|ππ (π₯π ), π₯π = 1, πππ€, π΅π|πΆmax , where πππ€ represents a renewable resource and π΅π reinforces that consumption occurs while this resource is being used as a ‘‘speed-up’’ mechanism for the processing times. A DP algorithm is proposed to solve the problem, which is partitioned into two knapsack problems, however the DP does not contribute efficiently to this objective and a DP-based FPTAS is provided instead. The complexity of the DP algo∑ rithm is bounded by π(ππ ), where π = max{π΄, π΅}, π΄ = π∈π1 (ππ1 − ππ1 ) ∑ and π΅ = π∈π2 (ππ2 − ππ2 ). 17 Expert Systems With Applications 190 (2022) 116180 E.A.G.d. Souza et al. Table 11 Completion time related problems for parallel machines. Authors Baker and Merten (1973) Horowitz and Sahni (1976) Dessouky et al. (1990) Lee and Liman (1993) Alidaee (1993) Webster (1994) Cheng and Diamond (1995) Lee (1996) Alon et al. (1998) van Den Akker et al. (1999) Chen and Powell (1999b) Baptiste (2000) Lee and Chen (2000) Webster and Azizoglu (2001) Hall et al. (2001) Chen and Powell (2003) Ramachandra and Elmaghraby (2006) Mellouli et al. (2009) Kim et al. (2009) Zhao et al. (2009) Tang and Zhang (2011) Zhao and Tang (2014) Yoo and Lee (2016) Tadumadze et al. (2020) Problem notation ∑ π πβ₯ π€π πΉπ ∑ ππβ₯ π€π πΉπ ∑ ππβ₯ π€π πΉπ ∑ ππ|ππ , πππ = 1| πΆπ ∑ π 2|π2 ≤ πΎ| πΆπ ∑ π 2β₯ π€π πΉπ ∑ ππβ₯ π€π πΉπ ∑ π π|π½π | πΆπ ∑ π 2|π − π| π€π πΆπ ∑ π 2|ππ − π| π€π πΆπ ∑ π πβ₯ π (πΆπ ) ∑ π πβ₯ π€π πΆπ ∑ π πβ₯ π€π πΆπ ∑ ππβ₯ π€π πΆπ ∑ π πβ₯ π€π πΆπ ∑ π π|ππ = π, ππ | π€π πΆπ ∑ π π|ππ − π, πππ| π€π πΆπ ∑ π π|ππ − π, πππ| π€π πΆπ ∑ π π|ππΌπ | π€π πΆπ ∑ π π|ππΌπ | π€π πΆπ ∑ π π|ππ | πΆπ ∑ π π|ππ , π = π | πΆπ ∑ π π|ππ , π = π | π€π πΆπ ∑ π π|ππΌπ | π€π ππ ∑ π π|ππ·π | π€π ππ ∑ π 2|ππππ| π€π πΆπ ∑ π π|β(ππ )| πΆπ ∑ π π|π − ππππ| πΆπ ∑ π 2|ππ (πΌπ )| π€π πΆπ ∑ π π|ππ (πΌπ )| π€π πΆπ ∑ π π|ππ | πΆπ ∑ π π|ππ − π, ππ (π π‘π )| π€π πΆπ ∑ π π|πππ| π€π πΆπ ∑ π π|πππ| πΆπ ∑ π π|πππ| πΆπ ∑ π π|πππ| π€π πΆπ ∑ π π|πππ, ππ = π| πΆπ ∑ π π|πππ, ππ = π| π€π πΆπ π π|ππ , π π |π€π πΉmax Complexity Method – – π(min{ππ π΅, 2π }) π(ππ2π+1 ) – ∑ π(π π€π ) – π(π2 π) ∑ π(π πππ π 2 πmax ) ∑ π(π πππ π 2 ) – ∑ π(π ππ ) 2∑ π(π π ) ∑ ππ π(π2 πππ ) ∑ 2 π(π πππ ) π(π2π+2 ) π(π2 π 2 ) π(π2 π 3 + ππ 4 π‘2 ) ∑ π(ππ π+1−π ππ ( π€π )π−1 ) ∑ π+2−π π ∑ π(ππ π ( π€ π + ππ ) π ) ∑ π−1 π(π( ππ ) ) ∑ π(π( ππ )ππ −1 ) ∑ π(π( ππ )ππ −1 ) π(π2 max{π‘2 π − π‘1 π + 1}) π(π2 max{π‘2 π − π‘1 π + 1}) – – ∑ π(π ππ ) ∑ π(π( max{ππ , πΌπ ππ })6 ) ∑ π(π( max{ππ , πΌπ ππ })3π ) ∑ π(π πππ ) ∏ ∏ ∏ π(π (π‘1π − π‘0 ) (π‘2π ( 1 + ππ )π )) π(ππ(π 1 + π 2 )π ) π(ππ 2π ππ ) 1 2 π(πππ π3 π π4 π π ) π(πππ π3 π π4 π π ) π((π + 1)3π ) π((π + 1)3π ) – DP and Heuristics DP DP and Approximation algorithm DP DP and Heuristic DP DP DP DP DP DP, ILP and PTAS Linear Relaxation with DP B&B with DP B&B with DP B&B with DP DP and Decomposition algorithm B&B with DP B&B with DP DP DP DP DP DP DP DP DP, BIP and GA DP, B&B and MILP LP-based Heuristic with DP DP DP Lagrangian relaxation with DP DP DP DP DP DP DP DP MIP, BB&C with BDP and Heuristic Li and Wang (2010) conduct a research regarding the π π|ππ |πΆmax considering the job assignment restriction constraint with a DP-based PTAS as solution method for an arbitrary number of machines and a DP-based FPTAS for a fixed number of machines. The algorithms are bounded by π(π|ππ β₯ππ |) (with |ππ |, |ππ | being assignment subsets for the last machine) and π(ππ+1 (1βπ)π ), respectively. Haned, Soukhal, Boudhar, and Tuong (2012) consider the problem of minimizing the makespan taking into account delay transportation and preemption constraints, which is denoted by π 2|πππππ¦, ππππ|πΆmax . Despite the paper focusing on a FPTAS, the authors also present a DP ∑ algorithm with π(π2 ππ ) complexity to solve the problem, which is derived from a DP formulation proposed for the π 2β₯πΆmax in this paper. Yoo and Lee (2016) develop DP procedures, which have been also applied to lateness and total completion times functions, and convey them to solve the π π|πππ|πΆmax , π π|πππ|πΆmax and π π|πππ, ππ = π|πΆmax problems with the same complexity achieved by the other criteria. Rudek (2017) discusses the influence on learning or aging effects regarding arbitrary functions of processing times to minimize the makespan. The author includes preliminary topics on continuous functions for the single machine environment and devises a pseudopolynomial DP algorithm for integer-valued functions, which is ∑ ∑ bounded by π(π( ππ )π ( ππ π (π))π ) as well as the real-valued. Ghalami and Grosu (2019) attempt a more sophisticated approach to finding solutions for the π πβ₯πΆmax problem, in which they resort to a parallel DP method to construct a PTAS. First a DP approach is designed in order to select all the machines where πΆmax does not surpass a given threshold and then the DP formulation is associated to a graph-like structure in order to determine how to proceed with the adaptation ∑ 2 to the parallel DP version with π((πβπ)(1βπ ) β ππ ). Tadumadze et al. (2020) investigate the π π|ππ , π π |πΆmax problem via the same methods used for the π€π πΏmax counterpart. The BB&C method shows an outstanding performance even for larger problems with 100 jobs and 25 machines (see Table 12). 5.5. Multi-criteria and additional objective functions Rothkopf (1966) describes a DP formulation to solve two problems related to the minimization of a linear waiting cost function in π uniform machines and a non-linear waiting cost function in π identical machines. This method is able to create π − 1 independent state variables, however the calculations reach exponential order. Gupta and Maykut (1973) develop a DP formulation for three waiting cost functions. For the linear and exponential cases, the authors prove that the allocation problem is reduced to a solving one sequencing problem per stage, however for non-decreasing monotonic general functions the same cannot be stated and exponential growth of π(2π ) order is reached. So (1990) derives three heuristic procedures to solve the ∑ π π|πππ | π ππ€π problem in order to maximize the reward by scheduling composed by πΌ job families and π½ job types. The first and second heuristics employ DP formulations with by finding an optimal schedule for each machine as a single machine problem (Sequential Heuristic) and assigning each machine to a set of jobs (Decomposition Heuristic). The algorithms present π(π½ ππΎ 2 ) and π(π½ π2 πΎ 2 + π½ π2 πΎ ln (ππΎ)), respectively. Krämer and Lee (1994) study optimality properties and complexity ∑ analysis for the π 2|ππ€ | (πΈπ + ππ ) problem and proves it to be NP-hard. The optimality properties are applied to the proposed algorithm that 18 Expert Systems With Applications 190 (2022) 116180 E.A.G.d. Souza et al. Table 12 Makespan problems for parallel machines. Authors Problem notation Complexity Method Horowitz and Sahni (1976) π 2β₯πΆmax ππβ₯πΆmax π πβ₯πΆmax π π|ππ |πΆmax π π|ππ , π = π |πΆmax π πβ₯πΆmax π πβ₯πΆmax π 2β₯πΆmax π 2|ππ (π₯π ), π₯π = 1, πππ€, π΅π|πΆmax π π|ππ |πΆmax π π|ππ |πΆmax π 2|πππππ¦, ππππ|πΆmax π π|πππ|πΆmax π π|πππ|πΆmax π π|πππ, ππ = π|πΆmax π π|π΄π|πΆmax π π|πΏπ|πΆmax π πβ₯πΆmax π π|ππ , π π |πΆmax ∑ π(min{π min{ πΆππ }, 2π }) ∑ π(min{π min{ πΆππ }, ππ }) π π(ππ(ππβπΏ) ) ∑ π(π( ππ )π−1 ) ∑ π(π( ππ )ππ −1 ) – – π(ππmax ) π(ππ ) π(π|ππ β₯ππ |) π(ππ+1 (1βπ)π ) ∑ π(π2 ππ ) π(ππ 2π ππ ) 1 2 π(πππ π3 π π4 π π ) π((π + 1)3π ) ∑ ∑ π(π( ππ )π ( ππ π (π))π ) ∑ π ∑ π(π( ππ ) ( ππ π (π))π ) ∑ 2 π((πβπ)(1βπ ) β ππ ) – DP and Approximation algorithm DP and Approximation algorithm Approximation algorithm with DP DP DP Beam Search with DP Heuristic with DP DP and FPTAS FPTAS with DP PTAS with DP FPTAS with DP DP and FPTAS DP DP DP DP DP PTAS with Parallel DP MIP, BB&C with BDP and Heuristic Jansen and Porkolab (2001) Hall et al. (2001) Ghirardi and Potts (2005) Tang and Luo (2006) Glass and Kellerer (2007) Kellerer and Strusevich (2008) Li and Wang (2010) Haned et al. (2012) Yoo and Lee (2016) Rudek (2017) Ghalami and Grosu (2019) Tadumadze et al. (2020) is partitioned into an π(π2 ππ€ ) complexity DP algorithm to schedule the jobs that fit in the due window interval and an absolute error bound heuristic method, which reduces the overall complexity of the algorithm. De, Ghosh, and Wells (1994) outline the complexity analysis for ∑ ∑ the π π|ππ = π| (πΌπ πΈπ + π½π ππ ) and π π|ππ = π| πΌπ πΈπ + π½π ππ + πΎπ πΏ(π) problems and prove their NP-hardness in the strong sense and their particular cases involving two machines are NP-hard. A pseudo-polynomial DP algorithm is provided for each problem based on the optimality properties and computational experiments are performed, indicating that the proposed DP formulation yields better results in terms of CPU ∑ times for the π π|ππ = π| (πΌπ πΈπ + π½π ππ ) problem. Chen and Powell (1999a) develop a complex scheme to analyze ∑ the π πβ₯ (πΌπ πΈπ + π½π ππ ). A branch and bound algorithm is proposed with a decomposition process via column generation process until each node of the tree can be examined as two single machines sub-problems ∑ which, in turn, rely on two DP algorithms of π(π2 ππ ) complexity to be solved optimally. Bartal, Leonardi, Marchetti-Spaccamela, Sgall, and Stougie (2000) apply the rounding DP method seen in Horowitz and Sahni (1976) ∑ to design a FPTAS to solve the π πβ₯πΆmax + πππππ problem. The DP formulation denotes optimal solutions for each instance and it is used to verify the approximation ratio of the FPTAS. Sun and Wang (2003) elaborate a DP algorithm based on the LPT priority rule to establish a initial indexation of jobs and define a recursive relation to compute the objective function for the ∑ π π|π€π = ππ ππ , ππ = π| π€π |πΆπ − π| problem. Since the DP is classified ∑ as a pseudo-polynomial algorithm with π(πππ π ( ππ )π−1 ) complexity, the problem is NP-hard in the ordinary sense. Furthermore, an additional study on heuristics is shown with calculation of error bounds. Chen (2004) elaborates a similar algorithmic structure to previous works on B&B solved via partition, decomposition,column generation and single machine problems. The last portion of this division generates two DP algorithms, one of which is employed on finding the solution ∑ ∑ for the π π|π(π₯π )| π€π ππ + πΊ(π₯π ) problem with π(π2 π‘max max{ππ − ππ }) complexity. A second DP algorithm is applied to the single machine problem generated via decomposition to find the solution for the ∑ ∑ ∑ π π|π(π₯π )| π€π πΆπ + πΊ(π₯π ) problem with π(π2 ππ ) complexity and based on the principle of optimality. Jansen and Mastrolilli (2004) incorporate PTASs to solve three problems related to makespan, in which three bi-criteria involving a cost function with respect to resource allocation. Among these, one of the PTASs, which is applied to the π π|ππ (π₯π )|(πΊ(π₯π ), πΆmax ≤ πΎ) uses a DP algorithm to reduce to a polynomial number the state space of the problem Sung and Vlach (2005) investigate the minimization the ∑ π πβ₯ (π·π + ππ ) problem by analyzing its complexity and classifying it as NP-hard in the strong sense. In addition to this analysis, the authors design an π(πππ+1 ) DP polynomial-time algorithm that consists of three steps and incorporates V-bounded structure properties. Li, Shen, Ghenniwa, and Wang (2005) work with a criterion that computes the weighted square sum of the difference between the real length of time on a given machine (π¦π ) and the predefined length of time on a given machine (π§π ). The problem is modeled as a 0–1 quadratic model and a DP formulation is provided in order to solve it. Rios-Solis and Sourd (2008) evaluate theoretical and practical aspects of an exponential search neighborhood algorithm for the ∑ π π|ππ = π| πΈπ + ππ problem. Optimality properties are presented and a DP approach, which is based on interchange operations of early and tardy jobs in the schedule, is given. This formulation is the main element to optimize the search of feasible sequences and, therefore, the algorithm’s complexity is mostly defined by the DP’s, which is dependent on number of allocations. Experiments are performed in a set of jobs with up to 150 and applied in π = {4, 8} with satisfactory results given the CPU times and the gap between upper and lower bounds. Kedad-Sidhoum et al. (2008) adapt their own approach of the single-machine problem with earliness-tardiness criterion and devise ∑ bounds for the π πβ₯ (πΈπ + ππ ) problem. Experimental results are provided for at most 90 jobs and 6 machines. The DP-based heuristic and the Lagrangian bound show the best results when compared to the remaining bounds and the heuristic yields the smallest gap with regard to CPU times that are close to those registered for the Lagrangian bound. Agnetis, Alfieri, and Nicosia (2009) resort to a bounding scheme to assess the quality of given heuristic to solve general problems whose functions are defined as max{π (πΆπ )}. Therefore, a bounding scheme is developed in order to provide a comparison with the proposed heuristics. Such scheme relies on the column generation technique, which, in turn, is divided to the level of a pricing algorithm that might be solved by a DP formulation or a DP-based heuristic. Experimental results are presented for πmax and πΆmax but we omit them since they are not part of the scope of our research. Leyvand, Shabtay, Steiner, and Yedidsion (2010) analyze a variety of problems involving resource consumption and earliness-tardiness criteria with controllable processing times. They develop a π(πππ+1 ) ∑ ∑ time DP algorithm to solve the π π|ππ (π₯π )| (πΈπ + ππ ) + πΊ(π₯π ) and a FPTAS is derived from a DP formulation for the remaining problems. Li and Yuan (2010) design a FPTAS and a polynomial time DP ∑ ∑ ∑ algorithm to solve π π|πππ, ππ (π‘)| π€π πΆπ + πππππ and π π|πππ, ππ (π‘)| πΆπ + 19 Expert Systems With Applications 190 (2022) 116180 E.A.G.d. Souza et al. ∑ πππππ problems, respectively. The FPTAS depends on a DP recursion, ∑ which can be computed in π(π( π log (1 + ππ )βπ)π ) complexity. The polynomial DP algorithm is an extension of the algorithm devised by Cheng and Sun (2009) for single machine environment and yields π(π2 ) complexity. Zhao and Lu (2013) analyze two distinct models involving twoπ΄ βΆ agent scheduling criterion. The first model is related to the π πβ₯πΆmax ∑ π΅ πΆmax ≤ πΎ and a DP algorithm is developed with π(πππ΄ ππ΅ ( ππ )π π΄ ∑ ( ππ )π ) as well as an FPTAS derived from it. An akin procedure is π΅ ∑ π΄ π΅ devised for the π πβ₯ πΆπ βΆ πΆmax ≤ πΎ with the previously mentioned complexity. Dong (2013) aims at minimizing functions that are related to machine setup costs, job processing and energy consumption considering that the maintenance intervals are set within the problem rather than being prespecified. A B&B algorithm is proposed and its inner mechanism falls under the set partition scenario, which is ultimately solved by a DP algorithm in conjunction with a column generation method. The algorithm is tested via computational experiments, which proves the method is efficient for medium sized problems. Rebai, Kacem, and Adjallah (2013) evaluate solutions for the ∑ ∑ π π|β(π)| π€π πΆπ + π»(π‘1 , π‘2 ) where π»(π‘1 , π‘2 ) represents the preventive maintenance cost. The solutions proposed rely on a B&B algorithm and a GA, which can be reinforced by applying a DP formulation in order to obtain better initial solutions for the heuristic. The authors show that for problems with up to 300 jobs and 5 machines, both algorithms produce high quality solutions within reasonable time. In addition, the use of DP enhances the GA performance regarding solution quality. Zhang and Lu (2016) design a theoretical analysis on the ∑ πππ π π|πππ, ππ |πΆmax + ππ problem. The authors propose a pseudopolynomial DP approach in conjunction with earliest release date (ERD) priority rule for indexation and also apply it to a special case denoted ∑ by π π|πππ, ππ , ππ = π|πΆmax + πππππ . Each problem presents, respectively, ∑ π π(ππ(πmax + ππ ) ) and π(ππ2π+1 ) complexities. Furthermore, a FPTAS is also offered as solution method for the first problem. Yin, Cheng et al. (2016) present a theoretical assessment for design∑ ing algorithms to solve two-competing agents π πβ₯( (πΌπ π·π + π½π ππ )π΄ , ∑ ∑ min (πΌπ π·π + π½π ππ )π΅ ) and π πβ₯( (πΌπ π·π + π½π ππ )π΄ , (πΌπ π·π + π½π ππ )π΅ ) problems. The authors develop a pseudo-polynomial DP algorithm for each case, including elimination properties to reduce the solutions state space and their complexities are bounded by π(πππ+1 ππ΅ ) and π΄ ∑ ∑ π(π2 ππ+1 min{ (πΌπ + π½π )π΄ , (πΌπ + π½π )π΅ }), respectively. In addition, and FPTAS is derived from the DP approach for the last problem. Chen, Sterna, Han, and Blazewicz (2016) evaluate online and of∑ fline scheduling problems stemming from the π 2|ππ = π| ππ . The authors prove the given problem is NP-hard, however a simple pseudopolynomial DP algorithm with π(ππ 2 ) complexity is provided. In addition, they also state how close this problem is to a knapsack problem/bin packing problem as well as how it can relate to the π 2β₯πΆmax problem. Sterna and Czerniachowska (2017) develop a PTAS in order to solve ∑ the π πβ₯ ππ . Its construction derives from adaptations made in a series of list algorithms and the DP formulation designed by Chen et al. (2016). Dominance properties are concocted from relative improvements performed by observing the algorithms’ behavior and the PTAS is generated upon them so as to work in an optimal manner. Yin, Chen, Qin, and Wang (2019) devise a B&P algorithm to de∑ ∑ termine solutions for the two-agent π πβ₯ πΆπ π΄ βΆ π€π ππ π΅ problem. The solution method is composed of a three-step algorithm and an ∑ π(ππ΄ ππ΅ max{ππ΄ , ππ΅ } ππ ) DP forward recursion is used in order to provide solutions for the pricing sub-problem generated from a column generation method in each node. Furthermore, a dominance rule is also coupled to the DP in order to reduce the state space via fathoming. Experiments are performed for at most 80 jobs and 10 machines. Chen, Liang, Sterna, Wang, and BΕaΕΌewicz (2020) implement a DP and a FPTAS for solving the π π|ππ = π| max π·π problem. A theoretical analysis is carried out in order to deliver a complexity analysis and the results are tested computationally. Although DP might not be the best choice for solving this particular problem, it is relevant to state that a DP formulation is also integrated in the FPTAS in order to generate a modified instance that will be used as input for the algorithm, which have been experimented on at most 65 jobs and three machines. T’kindt, Shang, and Della Croce (2020) generate a theoretical al∑ ∑ gorithm for the π π|ππ = π ≥ ππ | π€π (πΈπ + ππ ) problem based on the DP across subsets and machines and Sort & Search algorithms in order to place the jobs. This ordering also relies on the use of an WSPT rule for the initial set of solutions and produces an π(3π ) time complexity DP formulation in the worst case. Additionally, this analysis can be extended to the uniform and unrelated parallel machines case, however the recursive relations needs to be adapted to such environments with no additional cost in terms of complexity (see Table 13). 5.6. Discussion on parallel machines problems Parallel machines problems that used DP as main or secondary methods did not follow a pattern either, as it was the case for single machine problems. One fact that can be noticed is that some of the methods that have been applied to single machine problems have been extended to parallel machines (e.g. Lawler & Moore, 1969). Furthermore, improvements have been made in order to consider a more realistic scenario, which can be seen, for example, in Tuong et al. (2010) by incorporating straddling jobs in the Lawler and Moore (1969) ∑ modeling of the problems involving π€π ππ . Problems involving more complex cases of parallel machines such as unrelated parallel machines and uniform parallel machines have also been investigated and despite their theoretical analysis, a series of open problems could be classified according to their computational complexity, as it is shown in Dessouky et al. (1990), Sung and Vlach (2005) and Tuong et al. (2010). Yet, the numbers for the identical parallel machines problems are far larger and even recent papers have been drawn to these types of machines, once they are less complex systems and therefore, the adherence of technological constraints or objective functions becomes more compatible. In terms of segmentation regarding objective functions, completion time-related criteria have dominated the topics of interest of the authors. Initially these problems concentrated on the unconstrained versions of flow time and completion times and on the early nineties, the inclusion of constraints started to appear, however a pattern could not be observed since they have varied from time to time. Nevertheless, some occurrences are indeed more frequent than others, as it is the case of dependent and independent cases of maintenance and also controllable processing times. Some authors have also made use of DP quite recurrently and consequently gained notoriety by studying adaptations of their initial approaches. Two that can be cited here are Baptiste, whose main interest was to apply a decomposition algorithm and derive a DP formulation from it in order to solve tardiness problems and those related to completion times (e.g. Baptiste, 2000). This author has also participated in works in single machine environments and flow shop scheduling and usually his papers discuss equal processing times. Chen’s papers have also received attention due to the decomposition method and column generation approach that would unfold into single machine problems that could be solved via DP (e.g. Chen & Powell, 1999a, 1999b). The recent trends in parallel machines are similar to those seen for single machine scheduling and they include more realistic objective functions and constraints, such as rejected jobs functions and constraints, multi-agent and hierarchical functions, just-in-time functions, resource allocation and costs, deteriorating jobs and maintenance. It is important to mention that the analysis for these problems remain theoretical for most cases when using DP due to the storage limitations associated to the Curse of Dimensionality. From this analysis, some conclusions can be drawn about the gaps that the studies in such environment have generated. Firstly, despite 20 Expert Systems With Applications 190 (2022) 116180 E.A.G.d. Souza et al. Table 13 Multicriteria and additional functions problems for parallel machines. Authors Rothkopf (1966) Gupta and Maykut (1973) So (1990) Krämer and Lee (1994) De et al. (1994) Chen and Powell (1999a) Bartal et al. (2000) Sun and Wang (2003) Chen (2004) Sung and Vlach (2005) Li et al. (2005) Rios-Solis and Sourd (2008) Kedad-Sidhoum et al. (2008) Agnetis et al. (2009) Leyvand et al. (2010) Li and Yuan (2010) Zhao and Lu (2013) Dong (2013) Rebai et al. (2013) Zhang and Lu (2016) Yin, Cheng et al. (2016) Chen et al. (2016) Sterna and Czerniachowska (2017) Yin et al. (2019) Chen et al. (2020) T’kindt et al. (2020) Problem notation ∑ π πβ₯ ππ π‘ ∑ ππβ₯ ππ (1 − π−ππ‘ ) ∑ π πβ₯ ππ π‘ ∑ π πβ₯ ππ (1 − π−ππ‘ ) ∑ π πβ₯ πΊ(π‘) ∑ π π|πππ | π ππ€π ∑ π π|πππ | π ππ€π ∑ π 2|ππ€ | πΈπ + ππ ∑ π π|ππ = π| πΌπ πΈπ + π½π ππ ∑ π π|ππ = π| πΌπ πΈπ + π½π ππ + πΎπ πΏ(π) ∑ π πβ₯ πΌπ πΈπ + π½π ππ ∑ π πβ₯πΆmax + πππππ ∑ π π|π€π = ππ ππ , ππ = π| π€π |πΆπ − π| ∑ ∑ π π|π(π₯π )| π€π ππ + πΊ(π₯π ) ∑ ∑ π π|π(π₯π )| π€π πΆπ + πΊ(π₯π ) ∑ π πβ₯ π·π + ππ ∑ π πβ₯ (π¦π − π§π )2 ∑ π π|ππ = π| πΈπ + ππ ∑ π πβ₯ (πΈπ + ππ ) π πβ₯ max{π (πΆπ )} ∑ ∑ π π|ππ (π₯π )| (πΈπ + ππ ) + πΊ(π₯π ) ∑ ∑ π π|πππ, ππ (π‘)| π€π πΆπ + πππππ ∑ ∑ π π|πππ, ππ (π‘)| πΆπ + πππππ π΄ βΆ πΆπ΅ ≤ πΎ π πβ₯πΆmax max ∑ π΅ ≤πΎ π πβ₯ πΆππ΄ βΆ πΆmax ∑ ∑ ∑ π π|β(π)| ππΆ(π‘) + πΈπΆ(π‘) + π½ π πΆ(π‘) ∑ ∑ π π|β(π)| π€π πΆπ + π»(π‘1 , π‘2 ) ∑ π π|πππ, ππ |πΆmax + πππππ ∑ π π|πππ, ππ , ππ = π|πΆmax + πππππ ∑ π πβ₯( (πΌπ π·π + π½π ππ )π΄ , min (πΌπ π·π + π½π ππ )π΅ ) ∑ ∑ π πβ₯( (πΌπ π·π + π½π ππ )π΄ , (πΌπ π·π + π½π ππ )π΅ ) ∑ π 2|ππ = π| ππ ∑ π π|ππ = π| ππ ∑ ∑ π πβ₯ πΆπ π΄ βΆ π€π ππ π΅ π π|ππ = π| max π·π ∑ ∑ π π|ππ = π ≥ ππ | π€π (πΈπ + ππ ) ∑ ∑ ππ|ππ = π ≥ ππ | π€π (πΈπ + ππ ) ∑ ∑ π π|ππ = π ≥ ππ | π€π (πΈπ + ππ ) Complexity Method – – – – π(2π ) π(π½ ππΎ 2 ) π(π½ π2 πΎ 2 + π½ π2 πΎ ln (ππΎ)) π(π2 ππ€ ) π(ππ(2π1 )π ) π(ππ[([πβπ] + 1)π1 ]2π ) ∑ π(π2 ππ ) – ∑ π(πππ π ( ππ )π−1 ) π(π2 π‘max max{ππ − ππ }) ∑ π(π2 ππ ) π(πππ+1 ) – – π(π2 ) – π(πππ+1 ) ∑ π(π( π log (1 + ππ )βπ)π ) 2 π(π ) ∑ ∑ π(πππ΄ ππ΅ ( ππ )ππ΄ ( ππ )ππ΅ ) ∑ ∑ π(πππ΄ ππ΅ ( ππ )ππ΄ ( ππ )ππ΅ ) – – ∑ π(ππ(πmax + ππ )π ) 2π+1 π(ππ ) π(πππ+1 ππ΅ ) π΄ ∑ ∑ π(π2 ππ+1 min{ (πΌπ + π½π )π΄ , (πΌπ + π½π )π΅ }) π(ππ 2 ) – ∑ π(ππ΄ ππ΅ max{ππ΄ , ππ΅ } ππ ) π(ππ π ) π(3π ) π(3π ) π(3π ) DP DP DP DP DP Heuristic with DP Heuristic with DP DP and Heuristic DP DP B&B with DP FPTAS with DP DP and Heuristic B&B with DP B&B with DP DP DP DP and Heuristic DP with Heuristic and LBs Bounding scheme with DP DP and FPTAS FPTAS with DP DP DP and FPTAS DP and FPTAS B&B with DP GA with DP and B&B DP and FPTAS DP DP DP and FPTAS DP PTAS with DP B&P with DP DP and FPTAS DP DP DP Fig. 3. Number of papers, separated by journal, that includes DP as solution method for parallel machine scheduling problems. the existence of DP applications in unrelated and uniform machines, the researches have been concentrating in the identical machines environment. Clearly, challenges may be found along the study due to the exponential nature that DP tends to incorporate, however, with the analysis developed by Woeginger (2000), FPTAS derived from DP could be designed. Furthermore, methods that have been promising for a given objective function could be extended with modifications for others, as it is the case of BCP method shown in Pessoa et al. (2010) and B&P algorithm seen in Lopes and de Carvalho (2007) for tardiness-related functions. As one can notice, no author has developed 21 Expert Systems With Applications 190 (2022) 116180 E.A.G.d. Souza et al. Fig. 4. Frequency of DP in parallel scheduling problems per journal. works in which DP was used as a subroutine of BCP or B&P for completion time-related functions and makespan and this could actually generate good results from both theoretical and practical standpoints. Additionally, decomposition methods have taken place regarding the parallel machine problems in several cases, which indicates that they could be exploited in recent topics that have been of interest, such as contemporary objective functions. As we can also notice, the computational experiments are also less frequent than the theoretical developments related to all types of parallel machine scheduling problems. Once again, the DP approach has given rise to a series of hybrid algorithms and also to new methods that are branched through alterations, being able to create more efficient resources in terms of CPU time and storage. Therefore, one of the main goals here would be to verify to which extent these methods can be applied and also to confirm their experimental limitations. We also highlight that a qualitative analysis concerning the journals that have published the articles in which DP has been presented as solution method for parallel machine scheduling problems might be needed. From Fig. 3, the journal that has presented a significant contribution regarding the characteristics stated above is the European Journal of Operational Research, which is accountable for 14.3% of the papers that described in this section, as it is shown in Fig. 4. Other journals have also contributed significantly in publishing the DP-related articles in the single machine environment, as it can be seen by the percentages attributed to them (Naval Research Logistics, Computers and Operations Research (7.9% each), Journal of Scheduling (6.3%) and Discrete Applied Mathematics and Computers and Industrial Engineering (4.8%)). Those that have shown less than 2% of contribution were placed in the ‘‘Others’’ category. In addition, one can tell that, compared to the single machine environment, there are less papers concerning DP, even though it is still a substantial amount. that, in this section, some of the criteria have been grouped in the same subsection due to a decrease in the number of articles involving DP and a specific criterion. 6.1. Classic due dates-related criteria ∑ Józefowska, Jurisch, and Kubiak (1994) address the πΉ 2|ππ = π| ππ problem among a series of shop environments and develop a study on the complexity proving it is ordinary NP-hard by association with a partition problem. In addition a π(ππ 2 ) pseudo-polynomial DP formalism is introduced as solution for the given problem. Sonmez and Baykasoglu (1998) incorporate the theoretical analysis ∑ of the πΉ π|π πππ | π€π ππ problem into a study case in a pipe manufacturing industry. The first part of the article is dedicated to introducing a DP formulation for the problem, which seems to be quite simple compared to some robust exact methods found in literature, although no complexity analysis is displayed. Sequentially, the authors employ the method to the pipe scenario and, due to the shop floor structure, they are able to convert the problem into a single machine and apply the DP formulation to solve the problem efficiently. Nishi and Hiranaka (2013) explore features of a Lagrangian relax∑ ation to solve the πΉ π|π πππ | π€π ππ problem. The algorithm undergoes a decomposition via machine capacity relaxation and a DP subroutine is proposed for its solution. Furthermore, the authors improve the lower bound by applying a cut generation method that also resorts to a DP subroutine. Experiments show that the algorithm is quite efficient for medium sized instances and they suggest the investigation of other methods to carry out more accurate cuts. ∑ Koulamas (2020) analyzes solutions for the πΉ π|πππ = ππ | ππ problem by developing a DP formalism, which is actually an extension from the one presented by Lawler (1977) by expanding the recursion method ∑ to π machines. The author proves the algorithm runs in π(π4 ππ ) and performs experiments for problems with up to 50 jobs and 20 machines (see Table 14). 6. Flow shop Flow shop scheduling has been an environment that, despite being far more complex compared to the ones previously outlined in this research, has received nearly undivided attention from most authors whose scheduling is a core theme and this interest can be traced back nearly to 70 years. Nevertheless, when seeking information on the contribution of dynamic programming in this environment, one can notice that only few authors have actually employed it as a primary or secondary method to solve several problems that compose the literature in flow shop scheduling and those are presented below. One may notice 6.2. Makespan and completion time-related criteria Corwin and Esogbue (1974) address the πΉ 2|π ππ |πΆmax problem by dividing it into two different problems that are characterized by the absence of sequence dependent setup times. When assuming the first one is allowed to present setup times, a backward DP formulation is proposed. Conversely, the authors offer a forward DP formulation for the problem where setup times are allowed on the second machine. 22 Expert Systems With Applications 190 (2022) 116180 E.A.G.d. Souza et al. Table 14 Due date related problems for flow shop. Authors Józefowska et al. (1994) Sonmez and Baykasoglu (1998) Nishi and Hiranaka (2013) Koulamas (2020) Problem notation ∑ πΉ 2|ππ = π| ππ ∑ πΉ π|π πππ | ππ ∑ πΉ π|π πππ | π€π ππ ∑ πΉ π|πππ = ππ | ππ Complexity Method π(ππ 2 ) – – ∑ π(π4 ππ ) DP DP Lagrangian relaxation with DP DP and FPTAS problems of main interest was the πΉ 2|β(π)|πΆmax problem and the authors develop a theoretical analysis on its complexity, which has been categorized as binary NP-hard with the manufacturing of a DP formulation that delivers the makespan in π(ππ 4 ), with π being the number of generated state variables dependent on the maintenance interval. Furthermore, a FPTAS can be derived from this approach to solve the same problem using the DP as a subroutine. Bautista, Cano, Companys, and Ribas (2012) delineate properties related to a DP-based heuristic, which is commonly known as Bounded Dynamic Programming (BDP), for solving the πΉ π|πππππ|πΆmax problem. It considers features of both DP (transition through states of given stage and dominance properties) and B&B (bounding scheme) to generate solutions and given some conditions, the method can actually be viewed as an exact method. The method is applied the Taillard benchmark (up to 500 jobs) and it actually improves some of the instances for the given problem. Shang, Lenté, Liedloff, and T’Kindt (2018) apply a DP algorithm to the πΉ 3β₯πΆmax in order to generate a Pareto frontier whose composition are vectors of non-dominated solutions based on the completion times of permutations π and π ′ . By employing these dominance rules, the DP is bounded by an π(3π ) complexity. Ozolins (2019b) improves the technique developed by Bautista et al. (2012) in order to fully guarantee the optimality of the BDP approach. The author devises three adapted lower bounds and uses a recursive procedure in order to consider as many solutions as possible without memory overreaching. Optimality is proved for 20 jobs and 10 machines in reasonable time and some cases with 20 machines. Mor, Mosheiov, and Shapira (2019) investigate three proportionate flow shop problems on two machines taking into account a threshold for the penalty incurred on rejected jobs and learning effect, aiming ∑ ∑ at minimizing πΆmax , πΆπ and πΆmax functions. Three DP algorithms are designed and, despite differing according to the objective function, their functioning mechanism is fairly similar since the main recursive equation determines which jobs are selected or rejected. Furthermore, the three problems are classified as NP-hard and the algorithms are bounded by an π(π2 πΎ) complexity. The authors also report their computational results for different learning factors and problems containing at most 50 jobs with efficient outcomes for medium-sized instances. Mor and Mosheiov (2021) devise a theoretical analysis on two ∑ problems, which are makespan-related (πΉ π|π(ππ ), πππππ ≤ π π΅|πΆmax and ∑ πππ ∑ πΉ π|π(ππ ), ππ ≤ π π΅| πΆmax ) and in order to carry it out two DP algorithms are generated. For the first problem, the solution is guaranteed once that all states are included, the process of rejecting or accepting a given job is verified and the processed jobs are ordered according to a dispatching rule involving the deteorating rate. Additionally the complexity generated by this algorithm is of π(ππ π΅) order. The second DP algorithm is similar ot the first one, however there are some slight changes regarding the recursive relation for the objective function (see Table 15). Furthermore, in order to reduce storage in each case, some dominance rules are also included in both cases and the authors are able to find optimal solutions for 15 job-instances. Dutta and Cunningham (1975) develop a theoretical study on mathematical formulations to describe the πΉ 2|ππ,π+1 |πΆmax with ππ,π+1 denoting a limited buffer scenario. First, the authors introduce a DP formulation in order to find optimal solutions for the problem and, although it might be considered a fairly realistic model, it is an expensive one from the computational requirements standpoint. Therefore, a reduction in its complexity is performed and a sub-optimal DP is presented. van de Velde (1990) devise a B&B algorithm that essentially converges to a Lagrangian Relaxation which, in turn, results in a linear ordering problem. In order to create a more efficient bound, a DP dominance rule in association with two other based on Johnson’s rule is applied to reduce the search tree. Kovalyov and Werner (1997) analyze theoretical aspects of the πΉ 2|ππ |πΆmax problem and devise a PTAS to compare with preliminary studies. The approach is based on a DP formulation that bear resemblance to those proposed by Lawler and Moore (1969), Rothkopf (1966) and has π(ππ(2π )π π 2π−2 ) complexity, being π a subset of π½ and π = ∑ ∑ max{ ππ1 , ππ2 }. Lee (1997) evaluates the πΉ 2|π − π(π1 )|πΆmax and πΉ 2|π − π(π2 )|πΆmax problems and a complexity analysis proves both problems are NP-hard. Furthermore, the author design a pseudo-polynomial DP algorithm for the problem with unavailability placed on machine 1. Although the method is deemed fairly strong, its complexity renders it not viable and Johnson-based heuristics are offered as alternative solutions. Lee (1999) also extends the analysis in Lee (1997) for the semiresumable case problem. A complexity analysis is stated about the NP-hardness of the problem, since it is considered a generalized problem of the non-resumable scenario. In addition, the results are the same found in its previous work regarding the DP formulation. Hou and Hoogeveen (2003) investigate the πΉ 3|πππ = ππ βπ π |πΆmax problems under the assumption that all machines operate under different speeds and machine 2 is the slowest one. An π(ππ 1 π 22 π 3 max{ππ }2 ) DP algorithm is proposed by incorporating V-shaped optimality properties as well as a recursive function that computes the makespan for subsequences. Furthermore, a combination of optimality properties and a series of lemmas prove that the problem can be classified as ordinary NP-hard. Bouquard, Billaut, Kubzin, and Strusevich (2005) develop a diversified research on problems involving number of regular and nowait jobs and methods are provided so as to solve them. Among them, the πΉ 2|πππ + ππ€π‘, ππππ’, πππ€π‘ = π|πΆmax can be solved via a pseudopolynomial time DP algorithm and a subsequent FPTAS (by converting the former approach). The complexity associated with the DP is of Μ 3π+1 ), where π Μ represents the maximum value among the form π(π(π) states generated when scheduling a given job. Allaoui, Artiba, Elmaghraby, and Riane (2006) investigate the effects of heuristics derived from Johnson’s algorithm and a DP model applied to the πΉ 2|π − π(π1 )|πΆmax and πΉ 2|ππ − π(π1 )|πΆmax problems. A complexity analysis is carried out for the pseudo-polynomial DP model and, despite containing an exponential component and the number of subsets in π½ , it performs significantly better than the formulation proposed by Lee (1997), since it does not depend on processing times. Kubzin and Strusevich (2006) investigate some shop problems considering unavailability for either one or two machines. One of the 6.3. Multi-criteria and additional objective functions Lawler and Moore (1969) also take interest in applying their DP knapsack functional equation to problems considering two machines with the intent of minimizing a general loss time function. This application of the recursion takes into account a given common due date and the formulation is bounded by a π(ππ 2 ) complexity. 23 Expert Systems With Applications 190 (2022) 116180 E.A.G.d. Souza et al. Table 15 Makespan and completion time related problems for flow shop. Authors Problem notation Complexity Method Corwin and Esogbue (1974) Dutta and Cunningham (1975) van de Velde (1990) Kovalyov and Werner (1997) Lee (1997) Lee (1999) Hou and Hoogeveen (2003) Bouquard et al. (2005) Allaoui et al. (2006) Kubzin and Strusevich (2006) Bautista et al. (2012) Shang et al. (2018) Ozolins (2019b) Mor et al. (2019) πΉ 2|π ππ |πΆmax πΉ 2|ππ,π+1 |πΆmax ∑ πΉ 2β₯ πΆπ πΉ 2|ππ |πΆmax πΉ 2|π − π(π1 )|πΆmax πΉ 2|π π − π(π1 )|πΆmax πΉ 3|πππ = ππ βπ π |πΆmax πΉ 2|πππ + ππ€π‘, ππππ’, πππ€π‘ = π|πΆmax πΉ 2|π − π(π1 )|πΆmax πΉ 2|β(π)|πΆmax πΉ π|πππππ|πΆmax πΉ 3β₯πΆmax πΉ π|πππππ|πΆmax πΉ 2|πΏπ, πππππ ≤ πΎ|πΆmax ∑ πΉ 2|πΏπ, πππππ ≤ πΎ| πΆπ ∑ πππ πΉ 2|πΏπ, ππ ≤ πΎ| πΆmax ∑ πΉ π|π(ππ ), πππππ ≤ π π΅|πΆmax ∑ ∑ πΉ π|π(ππ ), πππππ ≤ π π΅| πΆmax – – – π(ππ(2π )π π 2π−2 ) ∑ π(ππ‘11 ( πππ )2 πmax 1 ) ∑ π(ππ‘11 ( πππ )2 πmax 1 ) π(ππ 1 π 22 π 3 max{ππ }2 ) Μ 3π+1 ) π(π(π) π(2π1 π log π) π(ππ 4 ) – π(3π ) – π(π2 πΎ) π(π2 πΎ) π(π2 πΎ) π(ππ π΅) π(ππ π΅) DP DP and Sub-optimal DP DP PTAS with DP DP and Heuristic DP and Heuristic DP DP and FPTAS DP and Heuristics DP and FPTAS BDP DP BDP DP DP DP DP DP Mor and Mosheiov (2021) presented. Both algorithms are pseudo-polynomial with π(π2 (πΆ(π))4 πΎ 2 ) ∑ and π(π2 (πΆ(π))4 πΎ 2 πππ ) complexities, respectively. Luo, Chen, and Zhang (2012) outline a theoretical approach to the π΅ π΄ π΄ + ππΆ π΅ πΉ 2β₯πΆmax max and πΉ 2β₯πΆmax βΆ πΆmax ≤ πΎ problems, respectively. Approximation algorithms and a DP that is suitable for both situations are also presented and, due to the latter, the problems can be classified as weakly NP-hard. It might be valid to comment that the complexity of the DP approach is relies on variables denoted here by πππ΄ and πππ΅ , which are valued according to allocation in analogy with the partition problem. Shabtay and Bensoussan (2012) develop a serial analysis on shop problems for the earliness-tardiness minimization. One of the problems ∑ of interest is the πΉ 2β₯ (πΌπ πΈπ + π½π ππ ). Its solution relies on an algorithm whose DP is mainly used for updating the recursive function and partitioning the jobs in groups of early and tardy based on a ∑ dominance rule and bounded by π(π2 ππ1 ) complexity. The authors also provide an FPTAS with the DP applied as a fundamental element for its functioning. π΄ +πΌπΆ π΅ problem, taking Fan and Cheng (2016) consider the πΉ 2β₯πΆmax max into account a pseudo-polynomial DP algorithm that generates a partition of subsets depending on their start time to update the objective function, which is a four-dimension vector containing partial sequences and start times of both agents. The complexity of the problem is proven to be ordinary NP-hard and the algorithm’s complexity is given by ∑ ∑ ∑ π(π ππ1 ( ππ1 + ππ2 )2 ). Ultimately an approximation algorithm based on Johnson’s rule is also presented. Shang et al. (2018) extend their approach to the case with general ∑ functions πmax and ππ , which can display similar behavior to the makespan criterion. For the first class of problems, the dominance rule adds the objective function as an element to discard partial sequences and the complexity is associated with an exponential form of total ∗ feasible solutions of the Pareto frontier (π(4|π | )). The second group of functions is solved analogously and is bounded by π(5π ). Wang, Zhu, Fang, Chu, and Chu (2018) investigate a MILP model ∗ |π πΈπΆ problem, which is a problem that aims for the πΉ 2, π ππ |πΆmax at minimizing the total electricity cost function without altering the ∗ makespan value (hence the πΆmax being adopted as a constraint) and considering variable time-of-use tariffs to the manufacturing problem. A DP-based heuristic is developed as well for solving the problem with a fixed sequence by modeling the energy cost function as a recursive equation in terms of completion time. Such algorithm produces an optimal scheduling with π(ππ 4 ) time complexity, where π represents a given horizon. An ILS algorithm, a Johnson’s Rule-based heuristic and an ILSDP (which combines features of DP in the end of the solution given by) are also provided. Comparisons are established via computational experiments for at most 50 jobs and the results show that ILSDP can outperform the other methods in terms of solution quality T’kindt, Gupta, and Billaut (2003) furnish a variety of solution methods in order to solve the lexicographic bi-criteria problem denoted ∑ by πΉ 2β₯πΏππ₯(πΆmax , πΆπ ), which are divided into mathematical programming formulations, exact methods and heuristic. Among, those a DP formulation is created and its complexity is bounded by π(π π΅π2π ). Although the method is mathematically structured, the computational requirements are high enough to make it the worst option among the others, being able to solve optimally only problems with up to 17 jobs. Yeung, OΔuz, and Cheng (2004) propose a B&B and a heuristic to ∑ solve the πΉ 2|ππ€ | (πΈπ + ππ ) problem. The B&B is structure is connected ′ to an π(π (πΆ(π)+ππ′ 2 −π min )) DP formulation via a bounding scheme and computational experiments are performed in order to verify efficiency. Although optimal solutions are found for 15-job instances in about 5 min, the heuristic is able to find near-optimal solutions for instances as ten times as large in 20 s. BΕaΕΌewicz, Pesch, Sterna, and Werner (2005b) outline the proof ∑ for the NP-hardness associated to the πΉ 2|ππ = π| π€π ππ problem by transforming the partition problem into their scheduling problem. They also develop a general DP formulation with π(π2 π 4 ) time complexity, which is able to prove the problem can actually be classified as binary NP-hard. Furthermore, a comparison among the DP, an enumeration method and list algorithms can be seen in BΕaΕΌewicz, Pesch, Sterna, and Werner (2005a) and the authors claim that, even though DP cannot be discarded because it was used for classifying the problem, it might not be the best method compared to the other ones in terms of efficiency. Dawande, Gavirneni, and Rachamadugu (2006) compile a variety of algorithms with the intent of maximizing a reward function under a makespan constraint for a two-machine scenario. Similarities between the knapsack DP functional approach seen in Lawler and Moore (1969) and the proposed DP algorithm are established, being the latter an π(π2 πΎ 2 log π) pseudo-polynomial time algorithm. Moreover comparisons are made among the DP, MIP and heuristics and due to its complexity, the DP algorithm is the one with the worst performance. T’kindt, Croce, and Bouquard (2007) address the problem of minimizing the number of tardy jobs and finding the best common due date in order to optimize it according to a Pareto-optimum curve. The authors design a π-exact method and an ILP in order to verify their efficiency according to the experimental results. Furthermore, the problem is defined as ordinary NP-hard and a pseudo-polynomial DP of π(ππ 2 ) complexity is also formulated by merging Johnson’s rule with the method proposed by Józefowska et al. (1994). Yeung, OΔuz, and Cheng (2009) branch their research on the JIT framework and develop two DP algorithms to solve πΉ 2|ππ = ∑ ∑ π| (πΌπ π·π + π½π ππ ) and πΉ 2|ππ = π| (πΌπ π·π + π½π ππ )+πΉ (π) problems. First they prove both problems are NP-hard through a partition problem analogy and the optimality properties regarding the jobs positioning are 24 Expert Systems With Applications 190 (2022) 116180 E.A.G.d. Souza et al. Table 16 Multicriteria and additional functions problems for flow shop. Authors Lawler and Moore (1969) T’kindt et al. (2003) Yeung et al. (2004) BΕaΕΌewicz et al. (2005b) BΕaΕΌewicz et al. (2005a) Dawande et al. (2006) T’kindt et al. (2007) Yeung et al. (2009) Luo et al. (2012) Shabtay and Bensoussan (2012) Fan and Cheng (2016) Shang et al. (2018) Wang et al. (2018) Kovalev et al. (2019) Koulamas and Kyparisis (2021) Problem notation ∑ πΉ 2|ππ = π| πΉ (π‘) ∑ πΉ 2β₯πΏππ₯(πΆmax , πΆπ ) ∑ πΉ 2|ππ€ | (πΈπ + ππ ) ∑ πΉ 2|ππ = π| π€π ππ ∑ πΉ 2|ππ = π| π€π ππ ∑ πΉ 2β₯( π ππ€π , πΆmax ≤ πΎ) ∑ πΉ 2|ππ = π|π ( ππ , π) ∑ πΉ 2|ππ = π| (πΌπ π·π + π½π ππ ) ∑ πΉ 2|ππ = π| (πΌπ π·π + π½π ππ ) + πΉ (π) π΄ π΅ πΉ 2β₯πΆmax + ππΆmax π΄ βΆ πΆπ΅ ≤ πΎ πΉ 2β₯πΆmax max ∑ πΉ 2β₯ (πΌπ πΈπ + π½π ππ ) π΄ π΅ πΉ 2β₯πΆmax βΆ πΌπΆmax πΉ 3β₯πmax ∑ πΉ 3β₯ ππ ∗ |π πΈπΆ πΉ 2, π ππ |πΆmax ∑ πΉ 2|ππ€π‘, πππ = ππ | |πΆπ − πΆπ | ∑ πΉ π|ππ€π‘, π πππ|πΆmax + πππππ ∑ ∑ πΉ π|ππ€π‘, π πππ| πΆπ + πππππ ∑ ∑ πΉ π|ππ − ππππ, π πππ| πΆπ + πππππ Complexity Method π(ππ 2 ) π(ππ π΅2π ) π(π′ (πΆ(π) + ππ′ 2 − π π‘min )) π(π2 π 4 ) π(π2 π 4 ) π(π2 πΎ 2 log π) π(ππ 2 ) π(π2 (πΆ(π))4 πΎ 2 ) ∑ π(π2 (πΆ(π))4 πΎ 2 πππ ) ∑ π΄ ∑ π((ππ΄ + ππ΅ )( (ππ + πππ΄ ) + (ππ΄ + πππ΄ ))4 ) ∑ ∑ π π((ππ΄ + ππ΅ )( (ππ΄ + πππ΄ ) + (ππ΄ + πππ΄ ))4 ) π π ∑ π(π2 ππ1 ) ∑ ∑ ∑ π(π ππ1 ( ππ1 + ππ2 )2 ) ∗ π(4|π | ) π(5π ) π(ππ 4 ) π(π3 ) π(π3 ) π(π3 ) π(π3 ) DP DP, MIP and Heuristic B&B with DP and Heuristic DP DP, Enumeration method and Heuristic DP, MIP and Heuristics DP and Enumeration Methods DP DP DP and Approximation Algorithm DP and FPTAS DP and FPTAS DP and Approximation algorithm DP DP DP-based heuristics and Heuristics DP DP DP DP and, even though its average time might reach ten times more the value obtained by ILS, it is still a powerful algorithm and the trade-off might be acceptable. Kovalev, Kovalyov, Mosheiov, and Gerstl (2019) design a polynomial time DP algorithm of π(π3 ) complexity to minimize the total absolute deviation of completion times for a no-wait proportionate flow ∑ shop, also known as TADC, denoted by πΉ 2|ππ€π‘, πππ = ππ | |πΆπ − πΆπ |. The DP is based on computing the objective function for the partial sequences and find an optimal schedule based on a π -shaped structure and in case it cannot be found, the algorithm shifts into a heuristic. Experiments are performed for at most 300 jobs and the algorithm is able to find π -shaped schedules within few seconds on average. Koulamas and Kyparisis (2021) develop a theoretical analysis on flow shop problems involving the minimization of completion timesrelated functions associated with rejection penalties. The investigation ∑ πππ is able to model the problem πΉ π|ππ€π‘|πΆmax + ππ as a TSP and subsequently a DP polynomial time algorithm of π(π3 ) complexity is devised to solve a special case, which is derived by studying the ∑ πΉ π|π πππ, ππ€π‘|πΆmax + πππππ problem, where π πππ denotes semi-ordered jobs via a pyramidal sequencing (SPT-LPT). A similar algorithm is ∑ ∑ generated for the πΉ π|π πππ, ππ€π‘| πΆπ + πππππ problem with the same time complexity and as an additional gain, the authors prove that this ∑ ∑ algorithm also solves optimally the πΉ π|π πππ, ππ − ππππ| πΆπ + πππππ problem (see Table 16). Regarding the problems associated with the Curse of Dimensionality, it might be recommended to develop new dominance rules and some trimming-based algorithms that are able to reduce the state space of feasible solutions. It may be also relevant to devise DPbased heuristics (see Bautista et al. (2012)) or combination with other exact algorithms so as to establish a more efficient approach. Although heuristics do not guarantee optimality, recent applications of those have proven to yield high quality solutions and depend on exact methods as subroutines to generate initial solutions or to enhance intrinsic mechanisms of the method. Another suggestion is related to the number of machines analyzed by the authors. It is seen that most two-machine flow shop problems have been widely studied when DP is involved while formulations for the π-machine scenario have not been accounted as often. Logically, due to the difficulties associated with storage and also the behavior of such systems, their modeling might also become harder to conceive. However, some adaptations could be used and mathematical formulations in terms of recursive equations and complexity could be devised. Eve though these may wind up being not practical for computational experiments, they might serve as background for future studies regarding the π-machine problems. Finally, since not many computational experiments have been provided in the state-of-art references, it might be necessary to investigate more of that in future research. Once again, since DP adherence to other methods (exact and non-exact) is commonly resorted to, it may be interesting to evaluate the application and response of such methods in the flow shop environment as well as to compare their performance to other ones that are already present. Due to the smaller share of articles that compose this environment, it is expected that the number of papers also undergoes a reduction and it is in fact what occurs according to Fig. 5. Only 16 journals have aggregated material regarding the use of DP in the flow shop environment, whereas the previous environments have presented over 25 journals each. In addition, Operations Research Letters is accountable for the largest contribution, however, the European Journal of Operational Research still represent a substantial share in the total amount of papers, which totaled 29. These statements can be confirmed by analyzing also Fig. 6, which shows the percentage related to the occurrence of DP in the flow shop environment on journals up until 2020. 6.4. Discussion on flow shop scheduling problems Flow shop is actually considered the simplest version of the shop scheduling problems, however it is much more complex when compared to the models in the previous sections. Therefore, one might expect that the number of papers that are dedicated to this environment is considerably smaller, and this is, in fact, what happens. The first observation that one might be able to conclude is that the largest share of articles are concentrated in the multi-criteria and additional functions and this indicates that several gaps are yet to be filled regarding classic criteria when DP is taken into account as solution method. This generates a large scenario of possibilities for exploring DP features in the flow shop environment in terms of objective functions as well as technological constraints. Therefore, authors should focus on developing DP new or additional formulations for problems involving, for instance, release dates, no-idle, no wait, blocking, sequence dependent setup times, among others. Analogously, completion time-related functions and due date-related functions have accounted for a small number when compare to makespan and other functions, which means that this may also be a lead for future studies in the area with DP. 7. Job shop Job shop scheduling has also been an environment which has been a target for researchers due to the establishment of different routes 25 Expert Systems With Applications 190 (2022) 116180 E.A.G.d. Souza et al. Fig. 5. Number of papers, separated by journal, that includes DP as solution method for flow shop scheduling problems. Fig. 6. Frequency of DP in flow shop scheduling problems per journal. on distinct machines. Some studies have been developed since the sixties but contribution has grown quite moderately only in the eighties. Hence, when comparing the use of dynamic programming to other methods, there might not be numerous articles tying this method to such environment. In this section we outline these papers and, due to a shortage in the number of references, all the criteria will be summarized in Table 18. windows (TSPTW) and a heuristic to compose a B&B algorithm. The authors collaborate with a DP formulation to solve the TSPTW relaxations and they compare the effectiveness of such method to propagation methods that have also been provided. They develop experiments for small, medium and large sized problems and notice that it could perform well for small instances and suggest that such method can be improved for larger sets. Balas, Simonetti, and Vazacopoulos (2008) also develop an adapted Bottleneck Heuristic for the problem π½ π|π πππ , π π |πΆmax by reformulating it as an asymmetric TSPTW problem in order to solve a general problem with fixed deadlines and as consequence, this problem, with addition of precedence constraints, can be solved via a DP subroutine combined with feasibility check properties in order to reduce the state space for accepted solutions. An overall comparison indicates the approach is promising even for harder instances, hence it might be useful in further studies. Gromicho, Van Hoorn, Saldanha-da-Gama, and Timmer (2012) furnish a DP algorithm to solve the π½ πβ₯πΆmax problem since no other exact method had been provided as solution for it. The paper focuses on deriving a dominance rule in order to supplement the algorithm with the adequate formulation via Bellman’s principle and the authors, in 7.1. Classic due dates-related criteria Józefowska et al. (1994) describe a DP formulation for the ∑ π½ 2|ππ = π| π€π ππ in which the computation of the tardy jobs depends on a conditional formalism that groups the jobs according to their selection for being early or tardy. It is a backward recursive relation bounded by an π(ππ 3 ) complexity. 7.2. Makespan and completion time-related criteria Artigues and Feillet (2008) investigate the π½ π|π πππ |πΆmax by incorporating varied concepts such as graph disjunction and TSP with time 26 Expert Systems With Applications 190 (2022) 116180 E.A.G.d. Souza et al. be interesting to extend the method for number of tardy jobs or to develop adapted methods with backward and/or forward recursion for the tardiness-related objective functions. For the completion time-related criteria, one can notice that TSP with time windows has been a recurrent artifice in order to solve the unconstrained version for the π-machine makespan problem. Apparently, it has been considered a successful approach, as it can be seen in Ozolins (2018a). Therefore, this approach could be extended to other completion time functions by resorting to TSPTW. Another approach that could also be used is to adapt the BDP version proposed by Bautista et al. (2012) by including TSPTW. Despite being considered a DP-based heuristic, it has produced significant results for the flow shop case and could increase the number of job and machine instances for the job shop case, even if it does not reach the optimum for all the data in the benchmark. Regarding the approaches, it is noticed that most of them rely on the classic objective functions, even for the non-regular criteria (which tend to analyze the earliness-tardiness function and its variants). Therefore some considerations concerning more contemporary objective functions might be needed (e.g. multi-agent and job rejection). These attempt may be challenging, once job shop itself is clearly a less studied environment with scarce background in concentrated topics but this could also lead to more theoretical sources that, a posteriori, should be unfolded onto empirical analysis. The job shop environment, due to a reduced number of articles, has been represented only by seven journals, given that most titles have been published Annals of Operations Research, Computers and Operations Research and Journal of Scheduling as it is shown in Figs. 7 and 8. This reinforces the need for more publications that involve the job shop scheduling as well as the use of DP as solution method to several types of segments within this environment that could be of interest either in classic or contemporary approaches. order to optimize the DP due to the curse of dimensionality, consider optimality conditions that avert a full set of feasible solutions. Its π complexity is bounded by π(π2π max (π + 1) ) complexity and empirical results show that the proposed algorithm performs exponentially better than brute force. Ozolins (2018a) proposes a BDP algorithm, which can be considered an improvement of the DP algorithm presented by Gromicho et al. (2012), however including sequence dependent setup times. A tight bound is provided and also the selection of feasible solutions is based on the solution for the TSPTW seen in Artigues and Feillet (2008). Computational results show that the BDP solves to optimality and even achieve better solutions that the previous best known solutions in several benchmarks with at most 20 jobs and 10 machines. Ozolins (2018b) conducts a robust study on the π½ π|ππ€π‘|πΆmax problem. Two remarks must be made concerning the DP structure of the solution method. The first one is that de DP algorithm presents a dominance rule that is part of the dynamic programming graph-like definition. Additionally, a recursive formalism is also presented as well as a prominent bound. The results are proven to achieve optimality for moderate size of jobs and machines (10 × 10) from several benchmarks in seconds. 7.3. Multi-criteria and additional objective functions ∑ Wang, Luh, Zhao, and Wang (1997) examine the π½ πβ₯ (πΌπ πΈπ2 + π½π ππ2 ) problem considering that some machines can be grouped into a set π»ππ according to their capabilities and a given horizon πΏ. The authors design a Lagrangian relaxation method to solve the problem and it is split into sub-problems that are relative to each part of the objective function. A backward DP formulation is proposed to furnish ∑ a solution to the weighted tardiness and yields an π(πΏ |π»ππ |). Luh et al. (1998) also extend the complexity of the problem analyzed in Wang et al. (1997) with the inclusion of limited buffer, family dependent setup times and a long horizon. Their solution also relies on decomposing the problem and the relaxation occurs on the family constraints and machine capacity. In addition, a backward DP formulation is presented to solve the decomposed part of the Lagrangian relaxation and its concept can be extended to the constraints without further adjustments. Since similarities can be shared with Wang’s DP ∑ formalism, the complexity remains π(πΏ |π»ππ |). BΕaΕΌewicz, Pesch, Sterna, and Werner (2007) design a DP approach ∑ to find the optimal schedule for the π½ 2|ππ = π| π€π ππ problem in which the recursive equation is based on the positioning of jobs throughout the sequence depending on separation of subgroups of early and tardy jobs. The overall complexity is given by π(π3 π 11 ) and the problem is classified as binary NP-hard due to this construction of optimal solutions based on DP. Baptiste, Flamini, and Sourd (2008) bounds are based on precedence constraints relaxation and resource constraint relaxation for the ∑ π½ πβ₯ (πΌπ πΈπ + π½π ππ ). The second type, which relies on a time-indexed formulation of the problem with release dates on a single machine, can be solved by a DP approach and when experiments are performed, it can present advantage over the precedence type even for large sets of machines. The complexity for this relaxation is given by π(ππ (max{ππ + ∑ πππ })), where ππ is a subset of π½ considering jobs performing a given number of operations (see Table 17). 8. Open shop The randomness of the open shop environment has also turned this problem into one of the most interesting settings in machine scheduling, since its behavior can be considered an ordeal. Due to this fact, the use of exact methods in solving such method has been scarce or just theoretically conceived. Nevertheless, when verifying the application of dynamic programming in this scenario one can notice that an unexpected amount of papers concerning this topic might appear, which is surprising considering the storage issues readily associated with the DP algorithms. These articles have been organized as follows and, as in the previous sections, metaheuristics have not been included nor have been articles involving the dynamic and flexible scenarios. 8.1. Classic due dates-related criteria Brucker, Jurisch, Jurisch et al. (1993) address problems in which unit processing times are considered in the open shop environment. First several problems are proved to be solved under the assumption that some of the open shop problems can be transformed into identical parallel machine problems. Then, further results are presented, in which an π(π2 ) DP formulation is developed to construct an optimal schedule of all early jobs that can be assembled in block structures to ∑ solve the π2|πππ = 1| π€π ππ . Brucker, Jurisch, Tautenhahn et al. (1993) investigate the ∑ ππ|πππ = 1| π€π ππ problem by incorporating the findings regarding the open shop being transformed in parallel machine seen in Brucker, Jurisch, Jurisch et al. (1993). This needs to be done in order to apply the DP formulation, which is of π(π2 ππ+1 ) complexity, for the construction of an optimal scheduling according to the sequencing of early jobs in optimal manner and tardy jobs arbitrarily. 7.4. Discussions on job shop scheduling problems Similar to the observations made for the flow shop scheduling problems, due to the shortage of state-of-art references, it is expected that the possibilities of problems that can modeled via DP are larger and they could be implemented to a handful of classes of objective functions and technological constraints. For instance, only one article has been found for the due date-related criteria with an specific function, which is weighted number of tardy jobs. In this sense, it may 27 Expert Systems With Applications 190 (2022) 116180 E.A.G.d. Souza et al. Table 17 Problems in the job-shop environment. Authors Józefowska et al. (1994) Wang et al. (1997) Luh et al. (1998) BΕaΕΌewicz et al. (2007) Artigues and Feillet (2008) Balas et al. (2008) Baptiste et al. (2008) Gromicho et al. (2012) Ozolins (2018a) Ozolins (2018b) Problem notation ∑ π½ 2|ππ = π| π€π ππ ∑ π½ πβ₯ (πΌπ πΈπ2 + π½π ππ2 ) ∑ π½ π|ππ·π , ππ,π+1 | (πΌπ πΈπ2 + π½π ππ2 ) ∑ π½ 2|ππ = π| π€π ππ π½ π|π πππ |πΆmax π½ π|π πππ , π π |πΆmax ∑ π½ πβ₯ (πΌπ πΈπ + π½π ππ ) π½ πβ₯πΆmax π½ π|π πππ |πΆmax π½ π|ππ€π‘|πΆmax Complexity Method π(ππ 3 ) ∑ π(πΏ |π»ππ |) ∑ π(πΏ |π»ππ |) π(π3 π 11 ) – – ∑ π(ππ (max{ππ + πππ })) 2π π π(πmax (π + 1) ) – – DP Lagrangian relaxation with DP Lagrangian relaxation with DP DP B&B with DP Heuristic with DP Lagrangian relaxation with DP DP BDP DP Fig. 7. Number of papers, separated by journal, that includes DP as solution method for job shop scheduling problems. Fig. 8. Frequency of DP in job shop scheduling problems per journal. previous stage or calculate the completion time of a block of jobs on the ∑ second machine. Moreover, its complexity is given by π(π ππ2 ) and a FPTAS is also derived from it. ∑ Tautenhahn and Woeginger (1997) study the ππ|πππ = 1, ππ | πΆπ 2 by designing an π(π ) DP algorithm to solve it. First, some optimality properties regarding the ordering of jobs is presented according to a increasing monotonic behavior of completion times and a recursive 8.2. Makespan and completion times-related criteria Strusevich and Hall (1997) consider the minimization of makespan setting one of the machines as non-bottleneck (ππ΅). The problem is denoted by π2|ππ΅|πΆmax and the authors prove it to be ordinary NP-hard by developing a forward DP formulation that computes the makespan at each stage, which may either keep the value of the 28 Expert Systems With Applications 190 (2022) 116180 E.A.G.d. Souza et al. relation is introduced with real and bounded values for cases where the sequence follows the optimality conditions and it is infinite, otherwise. Shafransky and Strusevich (1998) analyze the problem of minimizing the makespan by imposing that the jobs have to be scheduled according a given sequence on the last machine. According to Graham’s notation, the problem is denoted by π2|πΊπ(1)|πΆmax . Cases of preemption are considered, however, the DP algorithm is developed for the non-preemptive case. The algorithm allows partitions and deletion of some of these partitions ππ that might correspond to partial infeasible ∑ sequences. The algorithm’s complexity is given by π(π ππ1 ππ ) and a FPTAS is provided considering a DP subroutine based on the previous formulation. Guéret and Prins (1999) develop a lower bound for the problem ππβ₯πΆmax in which one of the steps that consist the B&B algorithm is to calculate values that work as lower and upper bounds for the completion times. By doing that, the authors create an analogy with the subset-sum problem and apply a DP algorithm, which solves it quickly, and therefore, the DP is viewed as a subroutine. Li (2011) considers a non-bottleneck machine under jobs deterioration regime. The author delineates optimality properties based on preliminary sources for obtaining an optimal schedule and apply those in order to devise a DP algorithm that is unfolded into two formulations depending on the route for scheduling a given job. Furthermore, the algorithm can be transformed in an FPTAS by reusing some optimality concepts. Zhang and Bai (2014) construct a lower bound by using Lagrangian ∑ relaxation for the ππβ₯ πΆπ2 problem. The problem is actually decomposed in two parts, being the first one relative to sequencing the operations and the second one to calculating the Lagrangian multipliers (referred to as assignment costs) via a forward DP formulation. The authors prove that the DP complexity is estimated as π(π max{π, π}πmax ) and it is appropriate for small-sized instances. Ozolins (2019a) apply a DP algorithm by relying on dominance rules and a lower bound to find optimal solutions for the ππβ₯πΆmax problem. These features are incorporated in order to reduce the state space compared to an enumeration method, which considers all possible schedules. In addition, the algorithm has its performance tested for problems with up to 7 jobs and 7 machines and, despite showing good results only for small-sized instances, the dominance rule can be useful in further research and it can assist on reducing a variety of solutions that can be disregarded. that include cases for idle and no-idle machines in order to apply the recursive relation and also a longest alternate processing times (LAPT) ∑ ∑ rule, producing an overall π(π( ππ1 + ππ2 )3 ) complexity. Moreover, since a DP pseudo-polynomial algorithm can be constructed for such problem, it is categorized as ordinary NP-hard (see Figs. 9 and 10). 8.4. Discussion on open shop scheduling problems The open shop scheduling problems solved via DP also represent a small compared to simpler environments. The papers gathered in this section shows us that the problems studied are diversified and this might represent potential for DP to be applied to this environment. Problems related with makespan and completion times-related criteria are those that account for the majority of research, which leads to a substantial background to develop further studies with these objective functions. On the other hand, the other objective functions cannot be accounted for a significant contribution and this might mean research in this area needs to be developed. Regarding the methods used, one can notice that they vary frequently. Also, combinations have been used in order to improve the efficiency of a given method or DP’s itself, as it can be seen in Guéret and Prins (1999) and Zhang and Bai (2014). It might be interesting to investigate some properties related to dominance rules and also the results of combining DP with heuristics in order to reduce the effects of storage intrinsic to DP. In addition, some of these may facilitate the use of DP in practical studies, which have not been developed widely and, those that have been, are only limited to very small instances. The qualitative analysis for the open shop environment shows that it has been represented by ten journals, and 25% of them have been published in the Operations Research Letters, as it is shown in Figs. 7 and 8. This, as it has been stated previously for the job shop discussion, reinforces the need for more publications that involve the open shop scheduling as well as the use of DP as solution method to several types of segments within this environment that could be of interest either in classic or contemporary approaches. 9. Concluding remarks DP is a method that, over the years, has been reinvented by the researchers in machine scheduling. Clearly it had to happen because of the drawbacks brought by the Curse of Dimensionality. These artifices used are usually adaptations made in order to make the original method more efficient and also in order to verify the adherence of DP to other methods, whether it is used as a primary tool or a secondary one. The studies developed for the single machine environment have shown that DP has undergone several transitions. We can notice that the first class of solutions relying on DP would focus on precedence rules and labeling schemes that have been introduced in due daterelated criteria problems (e.g. total tardiness and weighted total tardiness) by Baker (1977) and Schrage and Baker (1978). Even though these methods are reported to solve instances with a limited number of jobs, they inspired more efficient approaches such as the hybrid algorithms presented by Potts and Van Wassenhove (1982, 1987) that could solve problems at least three times larger in comparison to their predecessors. A second type of transition is seen with the adoption of different strategies to overcome the drawbacks inherent to DP (e.g. Carraway et al., 1992; Hariri & Potts, 1994; Potts & Van Wassenhove, 1992b), Woeginger (2000) represents a landmark on shifting procedures to alter DP formulations into FPTAS, which represents an important advance in algorithmic analysis. In summary, the last 20 years of research were focused on the development of new techniques to improve efficiency and on new heuristics derived from DP. This progress offered a background for more complex problems which are recurrent in industrial scenarios. It is worth noting that problems related to makespan, completion-times related criteria and non-regular functions have grown considerably. 8.3. Multi-criteria and additional objective functions BΕaΕΌewicz, Pesch, Sterna, and Werner (2004) present some problems characterized by minimization of late work criterion and variations, among which a DP formulation is provided as solution for ∑ the π2|ππ = π| π€π ππ problem. The algorithm is able to calculate the minimum total weighted late work based on parts of jobs that are processed earlier according to a common due date. Its complexity is bounded by π(ππ 2 min{πmax , π}) and due to the pseudo-polynomial nature of the algorithm, the problem is proven to be binary NP-hard. ∑ Zhang, Lu, and Yuan (2016) investigate the π2|πππ|πΆmax + πππππ problem by studying its complexity and proposing algorithms for solving it. Firstly, the problem is actually proved to be NP-hard even for unit processing times and equal rejection penalties. Then a DP algorithm is presented and its computation of the makespan depends on a recursive formulation that separates rejected from accepted jobs. Therefore, the problem and its aforementioned special cases can be classified as ordinary NP-hard due to this algorithm. Also, the complex∑ ∑ ity of the algorithm is estimated as π(π2 ( ππ1 )( ππ2 )) and, thereafter the approximation scheme is provided. Jiang, Zhang, Bai, and Wu (2018) develop a scheme similar to the one presented in Fan and Cheng (2016) so as to provide solutions for π΄ + πΌπΆ π΅ the π2β₯πΆmax max problem. A DP algorithm and an approximation algorithm are devised and the first one relies on optimal properties 29 Expert Systems With Applications 190 (2022) 116180 E.A.G.d. Souza et al. Table 18 Problems in the open-shop environment. Authors Brucker, Jurisch, Jurisch et al. (1993) Brucker, Jurisch, Tautenhahn et al. (1993) Strusevich and Hall (1997) Tautenhahn and Woeginger (1997) Shafransky and Strusevich (1998) Guéret and Prins (1999) BΕaΕΌewicz et al. (2004) Li (2011) Zhang and Bai (2014) Zhang et al. (2016) Jiang et al. (2018) Ozolins (2019a) Problem notation ∑ π2|πππ = 1| π€π ππ ∑ π2|πππ = 1| π€π ππ π2|ππ΅|πΆmax ∑ ππ|πππ = 1, ππ | πΆπ π2|πΊπ(1)|πΆmax ππβ₯πΆmax ∑ π2|ππ = π| π€π ππ π2|ππ΅, πππ (π‘)|πΆmax ∑ ππβ₯ πΆπ2 ∑ π2|πππ|πΆmax + πππππ π΄ π΅ π2β₯πΆmax + πΌπΆmax ππβ₯πΆmax Complexity Method π(π2 ) π(π2 ππ+1 ) ∑ π(π ππ2 ) π(π2 ) ∑ π(π ππ1 ππ ) – π(ππ 2 min{πmax , π}) – π(π max{π, π}πmax ) ∑ ∑ π(π2 ( ππ1 )( ππ2 )) ∑ ∑ π(π( ππ1 + ππ2 )3 ) – DP DP DP and FPTAS DP DP and FPTAS B&B with DP DP DP Lagrangian relaxation with DP DP and Approximation algorithm DP and Approximation algorithm DP Fig. 9. Number of papers, separated by journal, that includes DP as solution method for open shop scheduling problems. Special considerations such as controllable processing times, resource constraints, and job deterioration seem to be the core application of DP in recent years. DP-based algorithms such as SSDP and Guess-and-Check DP have also shown some promising results since the optimality conditions are maintained while inner drawbacks seem to exert a smaller impact when compared to the pure DP analysis. Additionally, theoretical algorithms and analysis were derived so as to include and classify problems related to contemporary functions and constraints (e.g. rejection, multiobjective functions as a combination of due date-related criteria, among others). Regarding parallel machines, the contributions of DP have been numerous, and patterns can be observed more closely than those present in the single machine environment. Some techniques have been extensively employed, which is the case of decomposition algorithms, Branch and Price methods, Branch and Cut methods, among others (e.g. Chen & Powell, 1999b; Lopes & de Carvalho, 2007; Pessoa et al., 2010). For this machine environment, most papers are based on a theoretical approach. This type of contribution permits the identification of optimality conditions as well as structural properties that can be incorporated into heuristics to reduce their search space. The most recent topics that entangle DP and parallel machines have been those related to constraints such as bounded resources, job rejection, job deterioration and controllable processing times. Regarding the objective functions, most of them is associated with the contemporary analysis brought by the industrial scenario, such as earliness-tardiness, number of early and tardy jobs, job rejection and multi-agent functions. One can also notice that those that are developed with a practical purpose are a junction of new DP formulations applied to routines that had already been presented in previous works (e.g. Yin et al., 2019). The largest share of papers involving flow shop environment have also addressed a more theoretical background rather than a practical one. Despite this fact, the problems that have been solved via DP can be divided into two classes: pure DP and DP-based algorithms. Applying pure DP to flow shop problems can, in fact, yield optimal solutions (e.g. T’kindt et al., 2003; Yeung et al., 2004), however the computational burden is still too high even for medium-sized instances in most cases. For problems with identical processing times, DP appears to present better results and find optimal solutions for instances with up to 50 jobs and 20 machines (e.g. Koulamas, 2020; Mor et al., 2019). On the other hand, DP-based algorithms seem to have adhered better to some flow shop problems such as BDP (e.g. Bautista et al., 2012), which has been able to find solutions of blocking flow shop for instances with up to 500 jobs. The theoretical approach of DP for flow shop problems follows the same trends of its predecessors by generating a series of FPTAS and complexity analysis associated with the algorithmic development. Also, it is notorious that for some cases, Johnson’s algorithm is modified to be applied as initial solution before developing some algorithms into full DP formulations. Additionally, some cases are also focused in devising dominance rules so as to reduce the state space created by DP. The considerations regarding job shop and open shop are minimum because DP has not been widely explored for these two environments. Some papers focused on solving the problem by using experimental 30 Expert Systems With Applications 190 (2022) 116180 E.A.G.d. Souza et al. Fig. 10. Frequency of DP in open shop scheduling problems per journal. tests and yielding solutions for up to 20 jobs in the job shop environment and 7 jobs in the open shop, leaving most observations to the theoretical analysis, which were mostly about the complexity associated either with the algorithm or the problem. Overall, these observations describe how DP has been applied over the years to the machine scheduling, however they also can help us list some gaps that have not been addressed in the papers concerning these two topics and how to suggest some improvements for future research themes. From our perspective, all the gaps and issues related to DP in machine scheduling can be summarized in three classes: Curse of Dimensionality, complexity of machine scheduling environments and theoretical versus practical analysis. The major drawback attributed to DP is the Curse of Dimensionality and when analyzing its effects on machine scheduling one can notice that they might occur due to the complex recursive relations generated when modeling the given machine scheduling problem. This can be explained because these relations often create algorithms with exponential complexity in terms of storage and tend to fail rapidly when solutions for large and even medium-sized problems are required. Again, to overcome this issue, it is necessary to appeal to hybrid algorithms where DP is commonly associated with Lagrangian relaxation, bounding schemes and dominance rules. Therefore, more research should be conducted to improve DP performance. For example, bounding schemes are versatile structures and therefore, being able to couple an already existing bound with a new bound to the DP formulation might yield better results than working with pure DP approach. It is also worth noting that it would be interesting to see more papers that explore dominance properties since they are fundamental aspects for improving the performance of DP algorithms. We are aware that most of the machine scheduling problems fall under the NP-hard category. Single machine and parallel machines are accountable for approximately 70% of the papers we gathered and the remaining 30% are relative to other shop floor environments. The main reason for that is that finding recursive are more challenging in relation to the structures of their formulations that need to be both mathematically and computationally feasible. To tackle this problem, we have seen that some algorithms have been branched from pure DP (e.g., BDP, SSDP, Guess-and-Check DP, Parallel DP) and, in some cases, they have shown better results when compared to pure DP, B&B, and MILP. When analyzing the structure of BDP and SSDP, for example, one can notice that they construct a codependency on bounding schemes, window widths and dominance rules, thus reducing their need to completely depend on a recursive relation to solve the problems. Hence, since these derived methods have not been yet explored sufficiently on some complex environments (mostly job shop and open shop). For instance, when we refer to Tanaka et al. (2009), the authors managed not only to adapt the SSDP algorithm in Ibaraki and Nakamura (1994) but also improve its performance by including a powerful lower bound whose dominance was applied upon two adjacent jobs, a dominance for four adjacent jobs, a sub-gradient optimization for selecting the best Lagrangian multipliers and also a sophisticated upper bound that is coupled in the state space modifiers computation. All these elements combined with the relaxation property continuously reduce the gaps between upper and lower bounds, generating an exact method, however with a more efficient performance of a pure DP approach. Nevertheless, the same adaptations that the authors have designed are also the main challenge because the formulation of efficient bounding structures and modifiers tend to increase in complexity as environments and objective functions change. The same can be stated for the BDP algorithm, which has been frequently employed due to its dominance rules and bounding schemes. Although Ozolins (2019b) has been able to enhance the quality of the algorithm proposed by Bautista et al. (2012) in terms of exactness, one of the main ordeals for this is that formulating Bellman’s equation for the πΉ π|πππππ|πΆmax has an significant computational cost. However, the state space cost associated can be reduced, as it is shown in Ma and Stachurski (2021) by altering the Bellman equation via practical sets of transformations, which maintain the optimality conditions but establish preferences according to a desired level of robustness or recursive characteristics. Additionally, some references in DP whose kernel are other problems in Operations Research might be useful for developing formulations for scheduling problems, as it is the case in Clautiaux, Detienne, and Guillot (2021) when resorting to SSDP to solve efficiently the knapsack problem but also confirming that various techniques used on their paper could be further adapted for other applications of SSDP (e.g. problems in scheduling involving precedence constraints). Lastly, as it can be noticed, most papers tend to address theoretical solutions to the scheduling problems and, therefore, the practical analysis of the method seems to be often neglected. Although this may strongly suggest that DP is not as practical, there are some points that should be considered: DP has largely contributed for unfolding the complexity of several problems in machine scheduling. This is relevant to comprehend how practical a given algorithm is and to guide researchers in search for improvements. Moreover, investigating 31 Expert Systems With Applications 190 (2022) 116180 E.A.G.d. Souza et al. theoretical analysis in DP is relevant because it is associated with new mathematical formulations that might be incorporated to the development of other practical algorithms that are unrelated to DP as well as future applications to DP and DP-based algorithms. In comparison with other exact methods, DP may not be a well explored field to tackle machine scheduling problems. However, it is important to mention that several advances in scheduling literature were possible due to the theoretical findings of studies that employ such technique. Moreover, future research trends include the hybridization of DP with heuristics to diminish the effects of the curse of dimensionality or the combination with other exact methods. 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