Research journal of Applied Sciences, Engineering and Technology 4(9): 1181-1197, 2012 ISSN: 2040-7467 © Maxwell Scientific Organization, 2012 Submitted: January 11, 2012 Accepted: February 09, 2012 Published: May 01, 2012 A Survey of the State of the Art in Particle Swarm Optimization 1 Mahdiyeh Eslami, 1Hussain Shareef, 2Mohammad Khajehzadeh and 1Azah Mohamed 1 Electrical, Electronic and Systems Engineering Department, University Kebangsaan Malaysia, Bangi, 43600, Selangor, Malaysia 2 Civil Engineering Department, Islamic Azad University, Anar Branch, Anar, Iran Abstract: Meta-heuristic optimization algorithms have become popular choice for solving complex and intricate problems which are otherwise difficult to solve by traditional methods. In the present study an attempt is made to review the one main algorithm is a well known meta-heuristic; Particle Swarm Optimization (PSO). PSO, in its present form, has been in existence for roughly a decade, a relatively short time compared with some of the other natural computing paradigms such as artificial neural networks and evolutionary computation. However, in that short period, PSO has gained widespread appeal amongst researchers and has been shown to offer good performance in a variety of application domains, with potential for hybridization and specialization, and demonstration of some interesting emergent behavior. This study comprises a snapshot of particle swarm optimization from the authors’ perspective, including variations in the algorithm, modifications and refinements introduced to prevent swarm stagnation and hybridization of PSO with other heuristic algorithms. Key words: Hybridization, modification, particle swarm optimization INTRODUCTION Optimization is ubiquitous and spontaneous process that forms an integral part of our day-to-day life. In the most basic sense, it can be defined as an art of selecting the best alternative among a given set of options. Optimization problems are widely encountered in various fields of science and technology such as engineering designs, agricultural sciences, manufacturing systems, economics, physical sciences, pattern recognition etc. in fact optimization techniques are being extensively used in various spheres of human activities, where decisions have to be taken in some complex situation that can be represented by a mathematical model. Optimization can thus be viewed as one of the major quantitative tools in network of decision making, in which decisions have to be taken to optimize one or more objectives in some prescribed set of circumstances. Sometimes such problems can be very complex due to the actual and practical nature of the objective function or the model constraints. In view of the practical utility of optimization problems there is a need for efficient and robust computational algorithms, which can numerically solve on computers the mathematical models of medium as well as large size optimization problem arising in different fields. Traditionally, optimization methods involved derivativebased techniques such as those summarized in (Echer and Kupferschmid, 1988; Momoh et al., 1999a; Momoh et al., 1999b). These techniques are robust and have proven their effectiveness in handling many classes of optimization problems. However, such techniques can encounter difficulties such as getting trapped in local minima, increasing computational complexity, and not being applicable to certain classes of objective functions. This led to the need of developing a new class of solution methods that can overcome these shortcomings. In the past few decades several global optimization algorithms have been developed that are based on the nature inspired analogy. These are mostly population based meta-heuristics also called general purpose algorithms because of their applicability to a wide range of problems. Global optimization techniques are fast growing tools that can overcome most of the limitations found in derivative-based techniques. Some popular global optimization algorithms include Genetic Algorithms (GA) (Holland, 1992), Particle Swarm Optimization (PSO) (Kennedy and Eberhart, 1995), Differential Evolution (DE) (Price and Storn, 1995), Evolutionary Programming (EP) (Maxfield and Fogel, 1965), Ant Colony Optimization (ACO) (Dorigo et al., 1991)etc. A chronological order of the development of some of the popular nature inspired meta-heuristics is given in Fig. 1. These algorithms have proved their mettle in solving complex and intricate optimization problems arising in various fields. Figure 2 shows the distribution of publications which applied the meta-heuristics methods to solve the optimization problem. This survey is based on ISI Web of Corresponding Author: Mahdiyeh Eslami, Electrical, Electronic and Systems Engineering Department, University Kebangsaan Malaysia, Bangi, 43600, Selangor, Malaysia 1181 Res. J. Appl. Sci. Eng. Technol., 4(9): 1181-1197, 2012 been shown to offer good performance in a variety of application domains, with potential for hybridization and specialization. It is a simple and robust strategy based on the social and cooperative behavior shown by various species like flock of bird, school of fish etc. PSO and its variants have been effectively applied to a wide range of benchmark as well as real life optimization problems. This paper aims to offer a compendious and timely review on the development of the PSO algorithm as a well known and popular search strategy. For the aim of this review, a literature overview has been carried out including the IEEE and ISI Web of Knowledge databases which are the largest abstract and citation databases of research literature and quality web sources. The survey spans over the last 10 years from 2001 to March 2011. Figure 3 statistically illustrates the number of published research papers on the subject of the PSO during the last 10 years. This paper presents a state of the art review of the previous studies which proposed modified versions of particle swarm optimization and applied them on various optimization problems arising in different fields. The review demonstrated that the particle swarm optimization and its modified versions have widespread application in complex optimization domains, and is currently a major research topic, offering an alternative to the more established evolutionary computation techniques that may be applied in many of the same domains. Fig. 1: Popular meta-heuristics in chronological order Fig. 2: Pie chart showing the publication distribution of the meta-heuristics algorithms 1600 Number of papers 1400 1200 1000 800 600 400 200 20 09 20 10 20 11 20 01 20 02 20 03 20 04 20 05 20 06 20 07 20 08 0 Year Fig. 3: The bar diagram of the number of PSO papers published in the year 2001 to 2011 Particle Swarm Optimization (PSO): The PSO algorithm is a population-based optimization technique belongs to category of the Evolutionary Computation (EC) for solving global optimization problems. Its concept was initially proposed by Kennedy as a simulation of social behavior and the PSO algorithm was first introduced as an optimization method in 1995 by Kennedy and Eberhart (1995). In a PSO system, multiple candidate solutions coexist and collaborate simultaneously. Each solution called a particle, flies in the problem search space looking for the optimal position to land. A particle, during the generations, adjusts its position according to its own experience as well as the experience of neighboring particles. PSO system combines local search method (through self experience) with global search methods (through neighboring experience), attempting to balance exploration and exploitation. A particle status on the search space is characterized by two factors: its position (Xi) and velocity (Vi). The new velocity and position of particle will be updated according to the following equations: Knowledge databases and included most of the papers that have been published during the past decade. PSO is a well known and popular search strategy has gained widespread appeal amongst researchers and has 1182 Vi k 1 Vi k C1 Rand . pbesti k X i k C2 rand . gbest k X i k (1) Res. J. Appl. Sci. Eng. Technol., 4(9): 1181-1197, 2012 Xi [k + 1] = Xi [k] + Vi [k + 1] (2) If Vi > Vmax, then Vi = Vmax If Vi < ! Vmax, then Vi = ! Vmax where, Vi = [vi,1, vi, 2, ..., vi,n] called the velocity for particle i, which represents the distance to be traveled by this particle from its current position; Xi = [xi,1,xi,2, ..., xi,n] represents the position of particle i; pbest represents the best previous position of particle i (i.e., local-best position or its experience); gbest represents the best position among all particles in the population X= [X1,X2, . . .,XN] (i.e. global-best position); Rand(.) and rand(.) are two independently uniformly distributed random variables with range [0, 1]; C1 and C2 are positive numbers parameters called acceleration coefficients that guide each particle toward the individual best and the swarm best positions, respectively. The first part of Eq. (1), Vi [k], represents particle’s previous velocity, which serves as a memory of the previous flight direction. This memory term can be visualized as a momentum, which prevents the particle from drastically changing its direction and biases it towards the current direction. The second part, C1 Rand (.) (pbesti [k]- Xi[k]), is called the cognition part and it indicates the personal experience of the particle. We can say that, this cognition part resembles individual memory of the position that was best for the particle. The effect of this term is that particles are drawn back to their own best positions, resembling the tendency of individuals to return to situations or places that were most satisfying in the past. The third part, C2rand (.) (gbest [k] -Xi [k]), represents the cooperation among particles and is therefore named as the social component. This term resembles a group norm or standard which individuals seek to attain. The effect of this term is that each particle is also drawn towards the best position found by its neighbor. After the PSO was issued, several considerations have been taken into account to facilitate the convergence and prevent an explosion of the swarm. A few important and interesting modifications in the basic structure of PSO focus on limiting the maximum velocity, adding inertia weight and constriction factor. Details are discussed in the following: Selection of maximum velocity: At each step of the iteration, all particles move to a new place, the direction and distance is defined by their velocities. It is not desirable in practice that many particles leave the search space in an explosive manner. Equation (1) shows that the velocity of any given particle is a stochastic variable and that it is prone to create an uncontrolled trajectory, allowing the particle to follow wider cycles in the design space, as well as letting even more escape it. In order to limit the impact of these phenomena, particle’s velocity should be clamped into a reasonable interval. Here the new constant Vmax is defined: Normally, the value of Vmax is set empirically, according to the characteristics of the problem. A large value increases the convergence speed, as well as the probability of convergence to a local minimum. In contrast, a small value decreases the efficiency of the algorithm whilst increasing its ability to search. Empirical rules require that for any given dimension, the value of Vmax could be set as half range of possible values for the search space. Research work from Fan and Shi and Eberhart (2001) shows that an appropriate dynamically changing Vmax can improve the performance of the PSO. Adding inertia weight: Shi and Eberhart (1998) proposed a new parameter w for the PSO, named inertia weight, in order to better control the scope of the search, which multiplies the velocity at the previous time step, i.e., Vi(t). The use of the inertia weight w improved performance in a number of applications. This parameter can be interpreted as inertia constant; Eq. (1) is now becomes: Vi k 1 w Vi k C1 Rand . pbesti k X i k C2 rand . gbest k X i k (3) Essentially, this parameter controls the exploration of the search space, so that a high value allows particles to move with large velocities in order to find the global optimum neighborhood in a fast way and a low value can narrow the particles’ search region. Initially the inertia weight was kept static during the entire search process for every particle and dimension. However, with the due course of time dynamic inertia weights were introduced. Constriction factor: When the particle swarm algorithm is run without restraining the velocity in some way, the system simply explodes after a few iterations. Clerc and Kennedy (2002) induced a constriction coefficient P in order to control the convergence properties of a particle swarm system. The value of the constriction factor is calculated as follows: 2 2 C C 2 4C , C1 C2 C 4.0 (4) with the constriction factor P, the PSO equation for computing the velocity is: 1183 Vi k C1 Rand . pbesti k X i k Vi k 1 C rand . gbest k X k i 2 (5) Res. J. Appl. Sci. Eng. Technol., 4(9): 1181-1197, 2012 The constriction factor results in convergence over time; the amplitude of the trajectory’s oscillations decreases over time. Note that as C increases above 4.0, P gets smaller. For instance, if C = 5 then P . 0.38 from Eq. (4), which causes a very pronounced damping effect. A normal choice is that C is set to 4.1 and the constant P is thus 0.729, which works fine. The advantage of using constriction factor P is that there is no need to use Vmax nor to guess the values for any parameters which govern the convergence and prevent explosion. The constriction approach is effectively equivalent to the inertia weight approach. Both approaches have the objective of balancing exploration and exploitation, and thereby improving convergence time and the quality of solution found. It should be noted that low values of w and P result in exploitation with little exploration, while large values result in exploration with difficulties in refining solutions (Alvarez-Benitez et al., 2005). As a member of stochastic search algorithms, PSO has two major drawbacks (Lovbjerg, 2002). The first drawback is that the PSO has a problem-dependent performance. This dependency is usually caused by the way parameters are set, i.e. assigning different parameter settings to PSO will result in high performance variance. In general, no single parameter setting exists which can be applied to all problems and performs dominantly better than other parameter settings. The common way to deal with this problem is to use self-adaptive parameters. Selfadaptation has been successfully applied to PSO by Clerc (1999), Shi and Eberhart (2001), Hu and Eberhart (2002), Ratnaweera et al. (2004) and Tsou and MacNish (2003) and so on. The second drawback of PSO is its premature character, i.e. it could converge to local minimum. According to Angeline (1998a,b), although PSO converges to an optimum much faster than other evolutionary algorithms, it usually cannot improve the quality of the solutions as the number of iterations is increased. PSO usually suffers from premature convergence when high multi-modal problems are being optimized. Several efforts have been made to advance a variation of PSO that have diminished the impact of the two aforementioned disadvantages. Some of them have already been discussed, including inertia weight, the constriction factor and so on. Further modifications as well as hybridization of the PSO with another kind of optimization algorithm are discussed in the next section. Modifications of the original PSO: After the PSO was discovered, it attracted the attention of many researchers for its beneficial features. Various researchers have analyzed it and experimented with it, including mathematicians, engineers, physicists, biochemists, and psychologists and many variations were created to further improve the performance of PSO. Unfortunately, even focusing on the PSO variants and specializations that, from our point of view, have had the most impact and seem to hold the most promise for the future of the paradigm, these are too numerous for us to describe every one of them. So, we have been forced to leave out some streams in particle swarm research. Van den Bergh and Engelbrecht (2002) proposed a new PSO algorithm with strong local convergence properties, called the Guaranteed Convergence Particle Swarm Optimizer (GCPSO) (van den Bergh and Engelbrecht, 2002). The new algorithm performs much better with a smaller number of particles, compared to the original PSO. Multi-start PSO (MPSO) which is an extension to GCPSO in order to turn it into a global search algorithm was proposed in (Van den Bergh, 200. Several versions of MPSO were proposed by Van den Bergh (2002) based on the criterion used to determine the convergence of GCPSO. The GCPSO is assumed to converge to a minimum if the counter reaches a certain limit. According to (Van den Bergh, 2002), MPSO generally performed better than GCPSO in most of the tested cases. Theoretically, if the swarm could be regenerated an infinite amount of times, the GCPSO could eventually find the global optimal. However, the performance of MPSO obviously degrades when the number of design variables in the objective function increases. He et al. (2004) presented a PSO with passive congregation (PSOPC) to improve the performance of Standard PSO (SPSO). Passive congregation is an important biological force preserving swarm integrity. By introducing passive congregation to PSO, information can be transferred among individuals of the swarm. This approach was tested with a benchmark test and compared with standard Gbest mode PSO, Lbest mode PSO and PSO with a constriction factor, respectively. Experimental results indicate that the PSO with passive congregation improves the search performance on the benchmark functions significantly. Padhye (2008) has collected strategies on how to select gbest and pbest. These strategies were originally designed for PSO to solve multi-objective problems with a good convergence, as well as diversity and spread along the Pareto-optimal front. However they can also be extended to other kinds of optimization problems. The author brings forward some new ideas about how to select gbest and pbest, together with the existing issues. Full Informed PSO (FIPSO) was introduced in 2004 by Mendes et al. (2004). The method is an alternative that is conceptually more concise and promises to perform more effectively than the traditional particle swarm algorithm. In this new version, the particle uses information from all its neighbors, rather than just the best one. Several variants are based on this 1184 Res. J. Appl. Sci. Eng. Technol., 4(9): 1181-1197, 2012 approach, such as: PSOOP (PSO with opposite particles) (Wang and Zhang, 2005), TSPSO (two-stage PSO) (Zhuang et al., 2008) , RDNPSO (random dynamic neighborhood PSO) (Mohais et al., 2008) , RDNEMPSO (randomized directed neighborhoods with edge migration in PSO) (Mohais et al., 2004) , PS2O (particle swarms swarm optimizer) (Chen et al., 2008) . Li (2004) proposed an improved PSO using the notion of species to determine its neighborhood best values, for solving multimodal optimization problems. In the proposed Species-based PSO (SPSO), the swarm population is divided into species subpopulations based on their similarity. Each species is grouped around a dominating particle called the species seed. At each iteration step, species seeds are identified from the entire population and then adopted as neighborhood bests for these individual species groups separately. Species are formed adaptively at each step based on the feedback obtained from the multimodal fitness landscape. Over successive iterations, species are able to simultaneously optimize towards multiple optima, regardless of if they are global or local optima. This approach was tested on a series of widely used multi-modal test functions and found all the global optima for the all test functions with good accuracy. An Adaptive Particle Swarm Optimization (APSO) on individual level was presented by Xie et al. (2002a) . By analyzing the social model of PSO, a replacing criterion based on the diversity of fitness between current particle and the best historical experience is introduced to maintain the social attribution of swarm adaptively by taking off inactive particles. As the evolution of swarm unfolds, the particles may loss the local and global search abilities when their individual best positions are very close to the best positions achieved from their neighbors which are called inactive particles. To overcome this issue, Xie et al. (2002b) defined a constant , as a measurement to detect inactive particles. Moreover, they proposed that the positions and velocities of the particles regenerated randomly. The testing of three benchmark functions using APSO indicates it improves the average performance effectively. Carvalho and Filho proposed Clan PSO (CPSO) (de Carvalho and Bastos-Filho 2009), which includes: C C Create clan topologies: Clans are groups of individuals, or tribes, united by a kinship based on a lineage or a mere symbolic. For each iteration, each clan performs a search and marks the particle that had reached the best position of the entire clan. Leader delegation: The process of marking the best within the clan is exactly the same as stipulating a clan’s symbol as guide. It is the same as delegating the power to lead the others in the group. C C Leaders’ conference: Leaders of all the clans exchange their information using Gbest or Lbest models. Clans feedback information: After the leaders’ conference, each leader will return to its own clan. The new information acquired in the conference will be spread widely within the clan. Results have shown that CPSO achieves better degrees of convergence. A new particle swarm optimizer, called Stochastic PSO (SPSO), which is guaranteed to convergence to the global optimization solution with probability one, is presented based on the analysis of the standard PSO (Cui and Zeng, 2004) . In this approach, if the global best position is replaced by a particle’s position in some interaction, this particles’ position will be regenerated and if a particles’ new position coincides with the global best position, its position will also be regenerated randomly. The authors have proved that this is a guaranteed global convergence optimizer and through some numerical tests this optimizer showed its good performance. He and Han (2006) presented PSO with disturbance term (PSO-DT) which add a disturbance term to the velocity updating equation based on the prototype of the standard PSO trying to improve (or avoid) the shortcoming of standard PSO. The addition of the disturbance term based on existing structure effectively mends the defects. The convergence of the improved algorithm was analyzed. Simulation results demonstrated that the improved algorithm have a better performance than the standard one. A modified particle swarm optimizer named Cooperative PSO (CPSO) was proposed by Van den Bergh and Engelbrecht (2004). The CPSO could significantly improve the performance of the original PSO by utilizing multiple swarms for optimizing different components of the solution vector by employing cooperative behavior. In this method, the search space is partitioned by dividing the solution vectors into smaller vectors, based on the partition several swarms will be randomly generated in different parts of the search space and used to optimize different parts of the solution vector. Then, two cooperative PSO models are proposed by the authors. In one of them (CPSO-Sk), a swarm with an ndimensional vector is divided into n swarms of onedimensional vectors and each swarm attempts to optimize a single component of the solution vector. In the other variant (CPSO-Hk), in each iteration, CPSO-Sk is implemented to obtain a sequence of potential solution points and half of those are randomly selected for an update with the original PSO. In case the new position dominates the previous one, the information of the sequence will be updated. Angeline (1998a, b) applied selection strategy to improve the performance of standard 1185 Res. J. Appl. Sci. Eng. Technol., 4(9): 1181-1197, 2012 PSO. In the proposed method, each particle was ranked based on a comparison of its performance compared with that of a group of randomly selected particles. A particle is awarded one point whenever it shows better fitness in a tournament than another. Members of the population are then organized in descending order according to their accumulated points. The bottom half of the population is then replaced by the top half. This step reduces the diversity of the population. The results show that the new approach performed better than the PSO (with and without w) in uni-modal functions. However, this approach performed worse than the PSO for functions with many local optima. Therefore, it can be concluded that although the use of a selection method improves the exploitation capability of the PSO, it reduces its exploration capability. In order to prevent premature convergence Xie et al. (2002a) Proposed Dissipative PSO (DPSO) by adding random mutation to PSO. This could be thought of as an inspiration for GA. DPSO introduces negative entropy through the addition of randomness to the particles. The results showed that DPSO performed better than standard PSO when applied to the benchmark problems. The concept of mutation is also adopted by other variants, such as: PSOG (PSO with gaussian mutation) (Higashi and Iba, 2003) , PSOM (PSO with mutation) (Stacey et al., 2003). Binary PSO (BPSO) was first proposed by Kennedy and Eberhart (1997). In this approach, the position in design space of each particle is expressed in a binary string. In the binary version, trajectories are changes in the probability that a coordinate will take on a zero or one value. Of course this approach can also be applied to continuous optimization problems, since any continuous real value can also be represented as a bit string. Jiao et al. (2008) proposed Improved Particle Swarm Optimization algorithm (IPSO) by introducing a dynamic inertia weight PSO algorithm for optimization problems. The algorithm used the dynamic inertia weight to decrease the inertia factor in the velocity update equation of the original PSO. The algorithm was tested with a set of 6 benchmark functions with 30, 50 and 150 different dimensions and compared with standard PSO, respectively. Experimental results indicated that the IPSO improves the search performance on the benchmark functions significantly. In order to keep the balance between the global exploration and the local exploitation validly, Jie et al. (2008) developed a Knowledge-based Cooperative Particle Swarm Optimization (KCPSO). KCPSO mainly simulates the self-cognitive and self-learning process of evolutionary agents in special environment, and introduces a knowledge billboard to record varieties of search information. Moreover, KCPSO takes advantage of multi-swarm to maintain the swarm diversity and tries to guide their evolution by the shared information. Under the guide of the shared information, KCPSO manipulates each sub-swarm to go on with local exploitation in different local area, in which every particle follows a social learning behavior mode; at the same time, KCPSO carries out the global exploration through the escaping behavior and the cooperative behavior of the particles in different sub-swarms. KCPSO can maintain appropriate swarm diversity and alleviate the premature convergence validly. The proposed model was applied to some wellknown benchmarks. The relative experimental results showed KCPSO is a robust global optimization method for the complex multimodal functions. In the other study, a Constrained Particle Swarm Optimization (CPSO) is developed by Azadani et al. (2010). In this method, constraint handling is based on particle ranking and uniform distribution. For equality constraints, the coefficient weights are defined and applied for initializing and updating procedure. This method applied to schedule generation and reserve dispatch in a multi-area electricity market considering system constraints to ensure the security and reliability of the power system. CPSO applied to three case studies and results showed promising performance of the algorithm for smooth and non smooth cost functions. Liu et al. (2007a) proposed center particle swarm optimization (Center PSO), which introduced a center particle into LDWPSO to improve the performance. Xi et al. (2008) introduced an improved Quantum-behaved PSO, which introduces a weight parameter into the calculation of the mean best position in QPSO in order to render the importance of particles in the swarm when they are evolving; this method is called Weighted QPSO (WQPSO). Yang et al. (2007) proposed another dynamic inertia weight to modify the velocity update formula in a method called modified Particle Swarm Optimization with Dynamic Adaptation (DAPSO). Ali and Kaelo (2008) presented an efficiency value to identify the cause for their slow convergence in PSO. Some modifications were proposed in the position update rule of PSO in order to make the convergence faster. Jiang et al.(2010) developed a shuffling master-slave swarm evolutionary algorithm based on particle swarm optimization (MSSE-PSO). The population is sampled randomly from the feasible space and partitioned into several sub-swarms (one master swarm and additional slave swarms), in which each slave swarm independently executes PSO. The master swarm is enhanced by the social knowledge of the master swarm itself and that of the slave swarms. For promoting any PSO variants, Tsoulos and Stavrakoudis (2010) proposed a stopping rule and similarity check in order to enhance the speed of all PSO variants. These PSO variants propose interesting strategies in terms of how to avoid premature convergence for sustaining the variety amongst 1186 Res. J. Appl. Sci. Eng. Technol., 4(9): 1181-1197, 2012 Table 1: A summary of modifications of the PSO Author/s Context Kennedy and Eberhart (1997) BPSO Angeline (1998a, b) Selection Van den Bergh and Engelbrecht (2002) Van den Bergh (2002) Xie et al. (2002a) GCPSO MPSO APSO He et al. (2004) Mendes et al. (2004) Li (2004) Cui and Zeng (2004) Van den Bergh and Engelbrecht (2004) PSOPC FIPSO SPSO SPSO CPSO Xie et al. (2002b) He and Han (2006) Liu et al. (2007a) Yang et al. (2007) Padhye (2008) Carvalho and Bastos-Filho (2009) DPSO PSO-DT Center PSO DAPSO MOPSO CPSO Jiao et al. (2008) Jie et al. (2008) Xi et al. (2008) IPSO KCPSO WQPSO Azadani et al. (2010) Jiang et al. (2010) CPSO MSSE-PSO Engelbrecht (2010) HPSO Chuang et al. (2011) C-Catfish PSO Brief introducing Discrete design variables are expressed in binary form in this variant. Particles are sorted based on their performance, the worst half is then replaced by the best half. Induce a new particle searching around the global best position found so far. Use GCPSO recursively until some stopping criteria is met. Improve swarm’s local and global searching ability by inserting self-organization theory. Add a passive congregation part to the particle’s velocity update formula. Use all particle i’s neighbors’ best personal position to update i’s velocity. Use several adaptively updated species-based sub swarms to search design space. Particle i’s position will be regenerated randomly if it is too close to the gbest. Use multi-swarms to search different dimensions of the design space by employing cooperative behavior. Add mutation to the PSO in order to prevent premature convergence. Induce a disturbance term to the velocity update formula. Introduce a center particle into LDWPSO Use dynamic inertia weight to modify the velocity update formula Utilize new selecting on strategies to get pbest and gbest. Use sub-swarms to search design space, sub swarms communicate with each other every some iterations. Introduce a dynamic inertia weight PSO algorithm for optimization problems Introduce a knowledge billboard to record varieties of search information introduces a weight parameter into the calculation of the mean best position in QPSO constraint handling is based on particle ranking and uniform distribution population is sampled randomly from the feasible space and partitioned into several sub-swarms particles are allowed to follow different search behaviors selected from a behavior pool introduced chaotic maps into catfish particle swarm optimization individuals, and also contain properties that ultimately evolve a population towards a higher fitness (global optimization or local optima). Chaotic catfish particle swarm optimization (C-CatfishPSO) is a novel optimization algorithm proposed by Chuang et al. (2011). Recently, numerous improvements, which rely on the chaos approach, have been proposed for PSO in order to overcome the disadvantage of the algorithm (Wang et al., 2001; Chuanwen and Bompard, 2005a, b; Liu et al., 2005; Xiang et al., 2007; Coelho and Mariani, 2009). CCatfishPSO introduced chaotic maps into catfish particle swarm optimization (CatfishPSO), which increase the search capability of CatfishPSO via the chaos approach. Simple CatfishPSO relies on the incorporation of catfish particles into PSO (Chuang et al., 2008). This effect is the result of the introduction of new particles into the search space (catfish particles), which replace particles with the worst fitness; these catfish particles are initialized at extreme points of the search space when the fitness of the global best particle has not improved for a certain number of consecutive iterations. This results in further opportunities of finding better solutions for the swarm by guiding the whole swarm to promising new regions of the search space (Chuang et al., 2008). In C-CatfishPSO, the logistic map was introduced to improve the search behavior and to prevent entrapment of the particles in a locally optimal solution. The introduced chaotic maps strengthen the solution quality of PSO and Catfish PSO significantly. Engelbrecht (2010) introduced a Heterogeneous PSO (HPSO). In the standard PSO and most of its modifications, particles follow the same behaviors. That is, particles implement the same velocity and position update rules and they exhibit the same search characteristics. In HPSO particles are allowed to follow different search behaviors in terms of the particle position and velocity updates selected from a behavior pool, thereby efficiently addressing the exploration-exploitation tradeoff problem. Two versions of the HPSO were proposed, the one static, where behaviors do not change, and a dynamic version where a particle may change its behavior during the search process if it cannot improve its personal best position. For the purposes of this preliminary study, five different behaviors were included in the behavior pool. A preliminary empirical analysis showed that much can be gained by using heterogeneous swarms. Recently the authors proposed the effective modifications to the original particle swam optimization algorithm and apply these modified techniques in the field of civil and electrical engineering (Eslami et al., 2010a, b, c, d, 2011a, b, c, d, e; Khajehzadeh et al., 2010a, b, 2011a, b, 2012). Also, Table 1 shows a summary of modifications of the PSO. 1187 Res. J. Appl. Sci. Eng. Technol., 4(9): 1181-1197, 2012 Hybridization of PSO algorithm: Hybridization is a growing area of intelligent systems research, which aims to combine the desirable properties of different approaches to mitigate their individual weaknesses. A natural evolution of the population based search algorithms like that of PSO can be achieved by integrating the methods that have already been tested successfully for solving complex problems (Thangaraj et al., 2011). Researchers have enhanced the performance of PSO by incorporating in it the fundamentals of other popular techniques like selection, mutation and crossover of GA and DE. Also, attempts have been made to improve the performance of other evolutionary algorithms like GA, DE, and ACO etc. by integrating in them the velocity and position update equations of PSO. The main goal, as we see is to harness the strong points of the algorithms in order to keep a balance between the exploration and exploitation factors thereby preventing the stagnation of population and preventing premature convergence. A selection of hybrid algorithms in which PSO is one of the prime algorithms is briefly surveyed here. Hybridization with Evolutionary Algorithms (EAs), including GAs, has been a popular strategy for improving PSO performance. With both approaches being population based, such hybrids are readily formulated. Angeline (1998a, b) applied a tournament selection process that replaced each poorly performing particle’s velocity and position with those of better performing particles. This movement in space improved performance in three out of four test functions but moved away from the social metaphor of PSO. Brits et al. (2002) used GCPSO (van den Bergh and Engelbrecht, 2002) in their niching PSO (Niche PSO) algorithm. Borrowing techniques from GAs, the Niche PSO initially sets up sub-swarm leaders by training the main swarm using Kennedy and Eberhart (1997) cognition only model. Niches are then identified and a sub-swarm radius set; as the optimization progresses particles are allowed to join sub-swarms, which are in turn allowed to merge. Once particle velocity has minimized they have converged to their sub-swarm’s optimum. The technique successfully converged every time although the authors confess that results were very dependent on the swarm being initialized correctly (using Faure sequences). Robinson et al. (2002), trying to optimize a profiled corrugated horn antenna, noted that a GA improved faster early in the run, and PSO improved later. As a consequence of this observation, they hybridized the two algorithms by switching from one to the other after several hundred iterations. They found the best horn by going from PSO to GA (PSO-GA) and noted that the particle swarm by itself outperformed both the GA by itself and the GA-PSO hybrid, though the PSO-GA hybrid performed best of all. It appears from their result that PSO more effectively explores the search space for the best region, while GA is effective at finding the best point once the population has converged on a single region; this is consistent with other findings. Grimaldi et al. (2004) proposed a hybrid technique combining GA and PSO called Genetical Swarm Optimization (GSO) for solving combinatorial optimization problems. In GSO, the population is divided into two parts and is evolved with these two techniques in every iteration. The populations are then recombined in the updated population, that is again divided randomly into two parts in the next iteration for another run of genetic or particle swarm operators. Several hybridization strategies (static, dynamic, alternate, self adaptive etc.) were proposed for GSO algorithm and validated them with some multimodal benchmark problems in (Gandelli et al., 2007) and also the application of GSO has also been shown in (Gandelli et al., 2006; Grimaccia et al., 2007). Juang (2004) introduced a new hybridization of GA and PSO (HGAPSO) where the upper-half of the best-performing individuals in a population are regarded as elites. However, instead of being reproduced directly to the next generation, these elites are first enhanced. The group constituted by the elites is regarded as a swarm, and each elite corresponds to a particle within it. In this regard, the elites are enhanced by PSO, an operation which mimics the maturing phenomenon in nature. An improved GA called GA-PSO was proposed by Kim and Park (2006) by using PSO and the concept of Euclidean distance. In GAPSO, the performance of GA was improved by using PSO and Euclidian data distance on mutation procedure of GA. He applied his algorithm for obtaining the local and global optima of Foxhole function. A hybrid technique combining two heuristic optimization techniques, GA and PSO, was proposed for the global optimization of multimodal functions (Kao and Zahara, 2008). Denoted as GA-PSO, this hybrid technique incorporates concepts from GA and PSO and creates individuals in a new generation not only by crossover and mutation operations as found in GA but also by mechanisms of PSO. A Hybrid PSO (HPSO) was proposed (Shunmugalatha and Slochanal, 2008), which incorporates the breeding and subpopulation process in GA into PSO. The implementations of HPSO to test systems showed that it converges to better solution much faster. A hybrid constrained GA and PSO method for the evaluation of the load flow in heavy-loaded power systems was developed by Ting et al. (2008). The new algorithm was used to find the maximum loading points of three IEEE test systems. A Hybrid algorithm called GA/PSO was proposed for solving multi-objective optimization problems and validated their algorithm on test problems and also on engineering design problems (Jeong et al., 2009). In this 1188 Res. J. Appl. Sci. Eng. Technol., 4(9): 1181-1197, 2012 algorithm, the first multiple solutions are generated randomly as an initial population and objective function values are evaluated for each solution. After the evaluation, the population is divided into two subpopulations one of which is updated by the GA operation, while the other is updated by PSO operation. Valdez et al. (2010) described a new hybrid approach for optimization combining PSO and GA using fuzzy logic to integrate the results of both methods and for parameters tuning. The new optimization method combined the advantages of PSO and GA to give us an improved FPSO + FGA hybrid approach. Fuzzy logic was used to combine the results of the PSO and GA in the best way possible. Premalatha and Natarajan (2009) proposed a discrete PSO with GA operators for document clustering. The strategy induces a reproduction operation by GA operators when the stagnation in movement of the particle is detected. They named their algorithm as DPSO with mutation and crossover. Abdel-Kader (2010) proposed GAI-PSO algorithm, which combines the standard velocity and position update rules of PSO with the ideas of selection and crossover from GAs. The GAI-PSO algorithm searches the solution space to find the optimal initial cluster centroids for the next phase. The second phase is a local refining stage utilizing the k-means algorithm which can efficiently converge to the optimal solution. Kuo and Lin (2010) proposed an evolutionary-based clustering algorithm based on a hybrid of GA and PSO for order clustering in order to reduce Surface Mount Technology (SMT) setup time. Hendtlass (2001) applied the DE perturbation approach to adapt particle positions. In this algorithm, named SDEA, particles’ positions are updated only if their offspring have better fitness. The DE reproduction process is applied to the particles in swarm at specified intervals. At the specified intervals, the PSO swarm serves as the population for DE algorithm, and the DE is executed for a number of generations. After execution of DE, the evolved population is further optimized using PSO. Zhang and Xie (2003) also used different techniques in tandem, rather than combining them, in proposed DEPSO. In this case the DE and canonical PSO operators were used on alternate generations; when DE was in use, the trial mutation replaced the individual best at a rate controlled by a crossover constant and a random dimension selector that ensured at least one mutation occurred each time. Kannan et al. (2004) applied DE to each particle for a finite number of iterations, and replaced the particle with the best individual obtained from the DE process. An algorithm named DEPSO was introduced by Talbi and Batouche (2004). It differs from the DEPSO algorithm proposed by Zhang and Xie (2003) as the DE operators are applied only to the best particle obtained by PSO. This algorithm was applied on medical image processing problem. Das et al. (2008) suggested a method of adjusting velocities of the particles in PSO with a vector differential operator borrowed from the DE family. In the proposed scheme the cognitive term is omitted; instead the particle velocities are perturbed by a new term containing the weighted different of the position vectors of any two distinct particles randomly chosen from the swarm. This differential velocity term is inspired by the DE mutation scheme and hence the authors name this algorithm as PSO-DV (particle swarm with differentially perturbed velocity). A hybrid of the barebones PSO and DE (BBDE) was proposed by Omran et al. (2009). DE was used to mutate, for each particle, the attractor associated with that particle, defined as a weighted average of its personal and neighborhood best positions. The performance of the proposed approach was investigated and compared with DE, a Von Neumann particle swarm optimizer and a barebones particle swarm optimizer. The experiments conducted show that the BBDE provides excellent results with the added advantage of little, almost no parameter tuning. Zhang et al. (2009) developed a hybrid of DE and PSO called DE-PSO, where three alternative updating strategies are used. The DE updating strategy is executed once in every l generations and if a particle’s best encountered position and the position of its current best neighbor are equal then random updating strategy is executed otherwise PSO updating strategy is used. A novel hybrid algorithm named PSO-DE was introduced (Liu et al., 2010), in which DE is incorporated to update the previous best positions of PSO particles to force them to jump out of local attractor in order to prevent stagnation of population. Caponio et al. (2009) proposed the super-fit memetic differential evolution (SFMDE) by hybridizing DE and PSO with two other local search methods; Nelder Mead algorithm and Rosenbrock algorithm. PSO assists the DE in the beginning of the optimization process by helping to generate a super-fit individual and then the local searches are applied adaptively by means of a parameter which measures the quality of super-fit individual. SFMDE was used for solving unconstrained standard benchmark problems and two engineering problems. An improved hybrid algorithm based on conventional PSO and DE (PSO-DE) was proposed (Khamsawang et al., 2010)for solving an economic dispatch problem with the generator constraints. In PSO-DE, the mutation operators of the DE are used for improving diversity exploration of PSO and are activated if velocity values of PSO are near to zero or violate the boundary conditions. Besides GA and DE, PSO has been hybridized with some other local and global search techniques as well. Shelokar et al. (2007) proposed a hybrid of PSO with ACO and called their algorithm 1189 Res. J. Appl. Sci. Eng. Technol., 4(9): 1181-1197, 2012 PSACO. It is a two stage algorithm, in which PSO is applied in the first stage and PCO is implemented in the second stage. Here, ACO works as a local search procedure in which the ‘ants’ apply the pheromone guided mechanism to update the positions found by the particles in the earlier stages. Hendtlass and Randall (2001) proposed a hybridization of PSO with ACO. A list of best positions found so far is recorded and the neighborhood best is randomly selected from the list instead of the current neighborhood best. More recently, Holden and Freitas (2008) introduced a hybrid PSO/ACO algorithm for hierarchical classification. This was applied to the functional classification of enzymes, with very promising results. Victoire and Jeyakumar (2004) hybridized PSO with another algorithm called Sequential Quadratic Programming (SQP) for solving economic dispatch problem. PSO was applied as a main optimizer while SQP was applied to fine tune the solution obtained after every PSO run. The best values obtained by PSO at the end of each iteration are treated as a starting point of SQP and are further improved with the hope of finding a better solution. Grosan et al. (2005) proposed a variant of the PSO technique named Independent Neighborhoods PSO (INPSO) dealing with sub-swarms for solving the well known geometrical place problems. In case of such problems the search space consists of more than one point each of which is to be located. The performance of the INPSO approach is compared with Geometrical Place Evolutionary Algorithms (GPEA). To enhance the performance of the INPSO approach, a hybrid algorithm combining INPSO and GPEA is also proposed. Chuanwen and Bompard (2005a, b) hybridized the chaotic version of PSO with linear interior point to handle the problems remaining in the traditional arithmetic of time consuming convergence and demanding initial values. They classified their algorithm into two phases; first the chaotic PSO is applied to search the solution space and then linear interior method is used to search the global optimum. Liu et al. (2007b) hybridized a Turbulent PSO (TPSO) with a fuzzy logic controller to produce a Fuzzy Adaptive TPSO (FATPSO). The TPSO used the principle that PSO’s premature convergence is caused by particles stagnating about a sub-optimal location. A minimum velocity was introduced with the velocity memory being replaced by a random turbulence operator when a particle exceeded it. The fuzzy logic extension was then applied to adaptively regulate the velocity parameters during an optimization run thus enabling coarse-grained explorative searches to occur in the early phases before being replaced by finegrained exploitation later. A hybridization of PSO with Tabu Search (TS) was proposed by Sha and Hsu (2006) for solving Job Shop Problem (JSP). They modified the PSO for solving the discrete JSP and applied TS for refining the quality of solutions. Another hybrid of PSO was suggested with Simulated Annealing (SA) for solving constrained optimization problems (He and Wang, 2007). SA was used to the best solution of the swarm to help the algorithm escape from local optima. Mo et al. (2007) proposed a new algorithm for function optimization problems, Particle Swarm assisted Incremental Evolution Strategy (PIES), which is designed for enhancing the performance of evolutionary computation techniques by evolving the input variables incrementally. In this version of PSO, the process of evolution is divided into several phases. Each phase is composed of two steps; in the first step, a population is evolved with regard to a certain concerned variable on some moving cutting plane adaptively. In the next step the better-performing individuals obtained from step one and the population obtained from the last phase are joined together in second step to form an initial population. Here, PSO is applied as a global phase while Evolutionary strategy is applied as a local phase. Fan et al. (2004) Fan and Zahara (2007) hybridized PSO with a well know local search namely Nelder Mead Simplex method and applied it for solving unconstrained benchmark problems. This hybrid version was named as NM-PSO, which was later extended for solving constrained optimization problems by Zahara and Kao (2009). Also a hybrid technique based on combining the K-means algorithm, NM-PSO, called K-NM-PSO, was applied to data clustering problem Kao et al., (2008). Another hybrid PSO algorithm for cluster analysis was proposed by Firouzi et al. (2008). PSO was integrated with SA and k-means algorithms. Shen et al. (2008) developed a hybrid algorithm of PSO and TS called HPSOTS approach for gene selection for tumor classification. TS was incorporated as a local improvement procedure to enable the algorithm to overleap local optima. A hybrid of PSO and Artificial Immune System (AIS) was introduced for job scheduling problem (Ge et al., 2008). An effective Hybrid Particle Swarm Cooperative Optimization (HPSCO) algorithm combining SA method and simplex method was proposed by Song et al. (2008). The main idea of HPSCO is to divide particle swarm into several sub-groups and achieve optimization through cooperativeness of different subgroups among the groups. Ramana et al. (2009) introduced a hybrid PSO, which combined the merits of the parameter-free PSO (pf-PSO) and the extrapolated PSO like algorithm (ePSO). Various hybrid combinations of pf-PSO and ePSO methods were considered and tested with the standard benchmark problems. Kuo (2009) presented a new hybrid PSO model named HPSO that combines a random-key encoding scheme, individual enhancement scheme, and PSO for solving the flow-shop scheduling problem. Chen et al. (2010) proposed a hybrid 1190 Res. J. Appl. Sci. Eng. Technol., 4(9): 1181-1197, 2012 Table 2: A summary of hybridized PSO with other optimization algorithms Author/s Context Hendtlass (2001) SDEA Hendtlass and Randall (2001) Robinson et al. (2002) GA-PSO & PSO-GA Wei et al. (2002) SFEP Zhang and Xie (2003) DEPSO Grimaldi et al. (2004) GSO Juang (2004) GAPSO Kannan et al. (2004) Talbi and Batouche (2004) DEPSO Victoire and Jeyakumar (2004) PSO-SQP Fan et al. (2004) NM-PSO Grosan et al. (2005) INPSO Chuanwen and Bompard (2005a, b) New PSO Sha and Hsu (2006) HPSO Gandelli et al. (2007) GSO Liu et al. (2007b) FATPSO He and Wang (2007) HPSO Mo et al. (2007) PIES Fan and Zahara (2007) NM-PSO Shelokar et al. (2007) PSACO Kao and Zahara (2008) GA-PSO Shunmugalatha and Slochanal (2008) HPSO Ting et al. (2008) CGA/PSO Das et al. (2008) PSO-DV Holden and Freitas (2008) PSO/ACO Kao et al. (2008) K-NM-PSO Firouzi et al. (2008) PSO-SA-K Shen et al. (2008) HPSOTS Ge et al. (2008) HIA Song et al. (2008) HPSCO Pant et al. (2008) AMPSO Cui et al. (2008) Hybrid algorithm Jeong et al. (2009) GanPSO Valdez et al. (2010) GanPSO Premalatha and Natarajan (2009) DPSO-mutation-rossover Omran et al. (2009) BBDE Zhang et al. (2009) DE-PSO Caponio et al. (2009) SFMDE Zahara and Kao (2009) NM-PSO Ramana et al. (2009) Pf-PSO, ePSO Kuo (2009) HPSO Kavehand and Talatahari (2009a) HPSACO Kavehand and Talatahari (2009b) DHPSACO Abdel-Kader EN.CITE(2010) GAI-PSO Kuo and Lin (2010) HGAPSOA Liu et al. (2010) PSO-DE Khamsawang et al. (2010) PSO-DE of PSO and Extremal Optimization (EO), called PSO-EO algorithm, where EO is invoked in PSO at l generation intervals (l is predefined by the user). A heuristic and discrete heuristic particle swarm ant colony optimization (HPSACO and DHPSACO) have been presented for optimum design of trusses by Kaveh and Talatahari (2009a, b). A Hybrid Harmony Search algorithm with swarm intelligence (HHS) to solve the dynamic economic load dispatch problem was introduced (Pandi and Panigrahi, 2011). This approach was an attempt to hybridize the HS algorithm with the powerful population Application Unconstrained global optimization Discrete optimization problems Engineering design Unconstrained global optimization Unconstrained global optimization Electromagnetic application Network design Generation expansion planning Medical image processing Power systems Multimodal functions Geometric place problems Power systems Job shop scheduling Unconstrained global optimization Unconstrained global optimization Constrained optimization Unconstrained global optimization Unconstrained global optimization Unconstrained global optimization Unconstrained global optimization Power system Power system Engineering design Data mining Data clustering Cluster analysis Gene selection and tumor classification Job shop scheduling industrial optimization Unconstrained global optimization Unconstrained global optimization Multi-objective optimization problems Unconstrained optimization problems Document clustering Unconstrained optimization problems Unconstrained optimization Unconstrained global optimization Engineering design Unconstrained global optimization Flow shop scheduling Engineering design Engineering design Data clustering Data clustering Constrained optimization and engineering problems Power systems based algorithm PSO for a better convergence of the proposed algorithm. Kayhan et al. (2010) proposed a new hybrid global-local optimization algorithm named PSOLVER that combines PSO and a spreadsheet “Solver” to solve continuous optimization problems. In the proposed algorithm, PSO and Solver are applied as the global and local optimizers, respectively. Thus, PSO and Solver work mutually by feeding each other in terms of initial and sub-initial solution points to produce fine initial solutions and avoid from local optima. The idea of embedding swarm directions in Fast Evolutionary 1191 Res. J. Appl. Sci. Eng. Technol., 4(9): 1181-1197, 2012 refinement of the approach and integration with other techniques, as well as applications moving out of the research laboratory and into industry and commerce. ACKNOWLEDGMENT The authors are grateful to Universiti Kebangsaan Malaysia (UKM) for supporting this study under grant UKM-DLP-2011-059. REFERENCES Fig. 4: Pie chart showing the distribution of publication of research articles having hybrid versions of PSO Programming (FEP) (Yao et al., 1999) to improve the performance of the latter was proposed by Wei et al. (2002). They applied their algorithm on a set of 6 unconstrained benchmark problems. The AMPSO algorithm proposed by Pant et al. (2008) is hybrid version of PSO including EP based adaptive mutation operator using Beta distribution. Another version of hybridizing PSO was suggested by Cui et al. (2008) by combining PSO with Fitness Uniform Selection Strategy (FUSS) and with Random Walk Strategy (RWS). The former strategy induces a weak selection pressure into the standard PSO algorithm while the latter helps in enhancing the exploration capabilities to escape the local minima. The summary of the main features of the hybridized PSO versions with other optimization algorithms are given in Table 2. The distribution of publication of research articles having hybrid versions of PSO is shown in Fig. 4 via pie chart. CONCLUSION PSO is a powerful optimization technique that has been applied to wide range of search and optimization problems. It has gathered considerable interest from the natural computing research community and has been seen to offer rapid and effective optimization of complex multidimensional search spaces. This review has considered the background and history of PSO and its place within the broader natural computing paradigm. The review then moved on to consider various refinements to the original formulation of PSO and modifications and hybridizations of the algorithm. These have been obtained by identifying and analyzing the publications stored in IEEE Xplore and ISI Web of Knowledge databases at the time of writing. The rate of growth of PSO publications is particularly amazing (Fig. 4). The number of publications reporting PSO applications has grown nearly exponential for the last few years. Clearly, the algorithm shines for its simplicity and for the ease with which it can be adapted to different application domains and hybridized with other techniques. The next decade will no doubt see further Abdel-Kader, R.F., 2010. Genetically improved PSO algorithm for efficient data clustering. In Proceedings of International Conference on Machine Learning and Computing, pp: 71-75. Ali, M. and P. Kaelo, 2008. Improved particle swarm algorithms for global optimization. Appl. Math. Comput., 196: 578-593. Alvarez-Benitez, J.E., R.M. Everson and J.E. Fieldsend, 2005. A MOPSO algorithm based exclusively on pareto dominance concepts. Proceedings of the 3rd International Conference on Evolutionary MultiCriterion Optimization, Guanajuato, Mexico, pp: 459-473. Angeline, P.J., 1998a. Evolutionary optimization versus particle swarm optimization: Philosophy and performance differences. Proceedings of the 7th Annual Conference on Evolutionary Programming, San Diego, USA, pp. 601-610. Angeline, P.J., 1998b. Using selection to improve particle swarm optimization. The IEEE International Conference on Evolutionary Computation Proceedings Anchorage, AK , USA, pp: 84-89. Azadani, E.N., S. Hosseinian and B. Moradzadeh, 2010. Generation and reserve dispatch in a competitive market using constrained particle swarm optimization. Int. J. Electr. Power Energ. Syst. 32: 79-86. Brits, R., A.P. Engelbrecht and F. Van den Bergh, 2002. A niching particle swarm optimizer. Proceedings of the 4th Asia-Pacific Conference on Simulated Evolution and Learning, pp: 692-696. Caponio, A., F. Neri and V. Tirronen, 2009. Super-fit control adaptation in memetic differential evolution frameworks. Soft Comput., 13: 811-831. Carvalho, D.F., C.J.A. Bastos-Filho, 2009. Clan particle swarm optimization. IEEE Congress on Evolutionary Computation, pp: 3044-3051. Chen, H., Y. Zhu, K. Hu and T. Ku, 2008. Global optimization based on hierarchical coevolution model. IEEE Congress on Evolutionary Computation, pp: 1497-1504. 1192 Res. J. Appl. Sci. Eng. Technol., 4(9): 1181-1197, 2012 Chen, M.R., X. Li, X. Zhang and Y.Z. Lu, 2010. A novel particle swarm optimizer hybridized with extremal optimization. Appl. Soft Comput., 10: 367-373. Chuang, L.Y., S.W. Tsai and C.H. Yang, 2008. Catfish particle swarm optimization. IEEE Swarm Intelligence Symposium, Louis, Missouri, pp: 1-5. Chuang, L.Y., S.W. Tsai and C.H. Yang, 2011. Chaotic catfish particle swarm optimization for solving global numerical optimization problems. Appl. Math. Comput., 217: 6900-6916. Chuanwen, J. and E. Bompard, 2005a. A hybrid method of chaotic particle swarm optimization and linear interior for reactive power optimisation. Math. Comput. Simulat., 68: 57-65. Chuanwen, J. and E. Bompard, 2005b. A self-adaptive chaotic particle swarm algorithm for short term hydroelectric system scheduling in deregulated environment. Energ. Convers. Manage., 46: 2689-2696. Clerc, M., 1999. The swarm and the queen: towards a deterministic and adaptive particle swarm optimization. Proceedings of the Congress on Evolutionary Computation, Washington D.C., USA, pp: 1951-1957. Clerc, M. and J. Kennedy, 2002. The particle swarmexplosion, stability, and convergence in a multidimensional complex space. IEEE Trans. Evolut. Comput., 6: 58-73. Coelho, L.S. and V.C. Mariani, 2009. A novel chaotic particle swarm optimization approach using Hénon map and implicit filtering local search for economic load dispatch. Chaos, Solitons Fract. 39: 510-518. Cui, Z., X. Cai, J. Zeng and G. Sun, 2008. Particle swarm optimization with FUSS and RWS for high dimensional functions. Appl. Math. Comput., 205: 98-108. Cui, Z. and J. Zeng, 2004. A guaranteed global convergence particle swarm optimizer. Proceedings of 4th International Conference on Rough Sets and Current Trends in Computing, Uppsala, Sweden, pp: 762-767. Das, S., A. Abraham and A. Konar, 2008. Particle swarm optimization and differential evolution algorithms: Technical analysis, applications and hybridization perspectives. Advances of Computational Intelligence in Industrial Systems, Studies in Computational Intelligence, pp. 1-38. De Carvalho, D.F. and C.J.A. Bastos-Filho, 2009. Clan particle swarm optimization. Int. J. Intell. Comput. Cybern., 2: 197-227. Dorigo, M., V. Maniezzo and A. Colorni, 1991. Positive feedback as a search strategy. Technical Report 91016, Dipartimento di Elettronica, Politecnico di Milano, IT, pp: 91-106. Echer, J. and M. Kupferschmid, 1988. Introduction to Operations Research, Wiley, New York. Engelbrecht, A., 2010. Heterogeneous particle swarm optimization. Proceeding of the 7th International Conference on Swarm Intelligence, pp: 191-202. Eslami, M., H. Shareef, A. Mohamed and S. Ghoshal, (2010). Tuning of power system stabilizers using particle swarm optimization with passive congregation. Int. J. Phys. Sci., 5(17): 2574-2589. Eslami, M., H. Shareef and A. Mohamed, 2011. Power system stabilizer design using hybrid multi-objective particle swarm optimization with chaos. J. Cent. South Univ. Technol., 18(5): 1579-1588. Eslami, M., H. Shareef and A. Mohamed, 2010. Optimal Tuning of Power System Stabilizers Using Modified Particle Swarm Optimization. Proceedings of the 14th International Middle East Power Systems Conference (MEPCON’10), Cairo University, Egypt, IEEE, pp: 386-391. Eslami, M., H. Shareef, A. Mohamed and M. Khajehzadeh, 2010. Improved particle swarm optimization with disturbance term for multi-machine power system stabilizer design. Aust. J. Basic Appl. Sci., 4(12): 5768-5779. Eslami, M., H. Shareef, A. Mohamed and M. Khajehzadeh, 2010. A hybrid PSO technique for damping electro-mechanical oscillations in large power system. In Proceeding, 2010 IEEE student conference on research and development engineering: Innovation and beyond, SCOReD 2010, Kuala Lumpur, Malaysia, 442-447 Eslami, M., H. Shareef, A. Mohamed and M. Khajehzadeh, 2011. Coordinated design of PSS and SVC Damping Controller Using CPSO. Proceedings of the 5th International Power Engineering and Optimization Conference (PEOCO2011), Malaysia, pp: 11-16 Eslami, M., H. Shareef, A. Mohamed and M. Khajehzadeh, 2011. Optimal location of PSS Using Improved PSO with chaotic sequence. Proceedings of the 1st International Conference on Electrical, Control and Computer Engineering (InECCE 2011), Kuantan, Malaysia. 253-258 Eslami, M., H. Shareef and A. Mohamed, 2011.Optimization and coordination of damping controls for optimal oscillations damping in multimachine power system. Int. Rev. Electr. Eng., 6(4): 1984-1993. Eslami, M., H. Shareef and A. Mohamed, 2011. Particle swarm optimization for simultaneous tuning of static var compensator and power system stabilizer. Prz. Elektrotechniczny (Electr. Rev.), 87(9 A) 343-347. Fan, H. and Y. Shi, 2001. Study of Vmax of the particle swarm optimization algorithm. In the Workshop on Particle Swarm Optimization, Indianapolis, IN: Purdue School of Engineering and Technology, pp: 1193 Res. J. Appl. Sci. Eng. Technol., 4(9): 1181-1197, 2012 Fan, S.K.S., Y. Liang and E. Zahara, 2004. Hybrid simplex search and particle swarm optimization for the global optimization of multimodal functions. Eng. Optimiz., 36: 401-418. Fan, S.K.S. and E. Zahara, 2007. A hybrid simplex search and particle swarm optimization for unconstrained optimization. Eur. J. Oper. Res., 181: 527-548. Firouzi, B., T. Niknam and M. Nayeripour, 2008. A new evolutionary algorithm for cluster analysis. World Academy of Science, Engineering, and Technology, pp: 605-609. Gandelli, A., F. Grimaccia, M. Mussetta, P. Pirinoli and R. Zich, 2007. Development and validation of different hybridization strategies between GA and PSO. In Proceedings of the IEEE Congress on Evolutionary Computation, pp: 2782-2787. Gandelli, A., F. Grimaccia, M. Mussetta, P. Pirinoli and R. Zich, 2006. Genetical swarm optimization: an evolutionary algorithm for antenna design. AUTOMATIKA, 47: 105-112. Ge, H.W., L. Sun, Y.C. Liang and F. Qian, 2008. An effective PSO and AIS-based hybrid intelligent algorithm for job-shop scheduling. IEEE Trans. Syst. Man Cybern., Part A: Syst. Hum., 38: 358-368. Grimaccia, F., M. Mussetta and R.E. Zich, 2007. Genetical swarm optimization: Self-adaptive hybrid evolutionary algorithm for electromagnetics. IEEE Trans. Antenn. Propag., 55: 781-785. Grimaldi, E.A., F. Grimaccia, M. Mussetta, P. Pirinoli and R. Zich, 2004. A new hybrid genetical-swarm algorithm for electromagnetic optimization. In Proceedings of International Conference on Computational Electromagnetics and its Applications, Beijing, China, pp: 157-160. Grosan, C., A. Abraham and M. Nicoara, 2005. Search optimization using hybrid particle sub-swarms and evolutionary algorithms. Int. J. Simul. Syst. Sc. Technol., 6: 60-79. He, Q. and C. Han, 2006. An improved particle swarm optimization algorithm with disturbance term. Comput. Intell. Bioinfo., 4115: 100-108. He, Q. and L. Wang, 2007. A hybrid particle swarm optimization with a feasibility-based rule for constrained optimization. Appl. Math. Comput., 186: 1407-1422. He, S., Q. Wu, J. Wen, J. Saunders and R. Paton, 2004. A particle swarm optimizer with passive congregation. Biosystems, 78: 135-147. Hendtlass, T., (2001). A combined swarm differential evolution algorithm for optimization problems. Proceedings of 14th International Conference on Industrial and Engineering Applications of Artificial Intelligence and Expert Systems, Lecture Notes in Computer Science, pp: 11-18. Hendtlass, T. and M. Randall, (2001). A survey of ant colony and particle swarm meta-heuristics and their application to discrete optimization problems. Proceedings of the Inaugural Workshop on Artificial Life, pp: 15-25. Higashi, N. and H. Iba, (2003). Particle swarm optimization with Gaussian mutation. In Proceedings of the IEEE Swarm Intelligence Symposium, SIS '03., pp: 72-79. Holden, N. and A.A. Freitas, (2008). A hybrid PSO/ACO algorithm for discovering classification rules in data mining. J. Artif evolut. Applied, 2008:1-11. Holland, J.H., (1992). Adaptation in natural and artificial systems: An introductory analysis with applications to biology, control, and artificial intelligence: The MIT Press, Hu, X. and R.C. Eberhart, 2002. Adaptive particle swarm optimization: detection and response to dynamic systems. In Proceedings of congress on Evolutionary Computation Hawaii, USA, pp: 1666-1670. Jeong, S., S. Hasegawa, K. Shimoyama and S. Obayashi, 2009. Development and investigation of efficient GA/PSO-hybrid algorithm applicable to real-world design optimization. IEEE Comput. Intell. Mag., 4: 36-44. Jiang, Y., C. Liu, C. Huang and X. Wu, 2010. Improved particle swarm algorithm for hydrological parameter optimization. Appl. Math. Comput., 217: 3207-3215. Jiao, B., Z. Lian and X. Gu, 2008. A dynamic inertia weight particle swarm optimization algorithm. Chaos, Solitons Fract., 37: 698-705. Jie, J., J. Zeng, C. Han and Q. Wang, 2008. Knowledgebased cooperative particle swarm optimization. Appl. Math. Comput., 205: 861-873. Juang, C.F., 2004. A hybrid of genetic algorithm and particle swarm optimization for recurrent network design. IEEE Trans. Syst. Man Cybern. Part B: Cybern., 34: 997-1006. Kannan, S., S.M.R. Slochanal, P. Subbaraj and N.P. Padhy, 2004. Application of particle swarm optimization technique and its variants to generation expansion planning problem. Electr. Power Syst. Res., 70: 203-210. Kao, Y.T. and E. Zahara, 2008. A hybrid genetic algorithm and particle swarm optimization for multimodal functions. Applied Soft Comput., 8: 849-857. Kao, Y.T., E. Zahara and I. Kao, 2008. A hybridized approach to data clustering. Exp. Syst. Appl., 34: 1754-1762. Kaveh, A. and S. Talatahari, 2009a. A particle swarm ant colony optimization for truss structures with discrete variables. J. Const. Steel Res., 65: 1558-1568. 1194 Res. J. Appl. Sci. Eng. Technol., 4(9): 1181-1197, 2012 Kaveh, A. and S. Talatahari, 2009b. Particle swarm optimizer, ant colony strategy and harmony search scheme hybridized for optimization of truss structures. Comput. Struct., 87: 267-283. Kayhan, A.H., H. Ceylan, M.T. Ayvaz and G. Gurarslan, 2010. PSOLVER: A new hybrid particle swarm optimization algorithm for solving continuous optimization problems. Exp. Syst. Appl., 37: 6798-6808. Kennedy, J. and R. Eberhart, 1995. Particle swarm optimization. Proceedings of the IEEE International Conference on Neural Networks, Piscataway, pp: 1942-1948. Kennedy, J. and R.C. Eberhart, 1997. A discrete binary version of the particle swarm algorithm. IEEE International Conference on Computational Cybernetics and Simulation, Orlando, FL , USA, pp: 4104-4108. Khamsawang, S., P. Wannakarn and S. Jiriwibhakorn, 2010. Hybrid PSO-DE for solving the economic dispatch problem with generator constraints. In Proceedings of the IEEE International Conference on Computer and Automation Engineering, pp: 135-139. Khajehzadeh, M., M. Taha and A. El-Shafie, 2010. Modified particle swarm optimization for probabilistic slope stability analysis. Int. J. Phys. Sci., 5(15): 2248-2258. Khajehzadeh, M., M.R. Taha, A. El-Shafie and M. Eslami, 2011. Modified particle swarm optimization for optimum design of spread footing and retaining wall. J. Zhejiang Univ-Sci. A (Appl Phys and Eng)., 12(6): 415-427. Khajehzadeh, M., M. Taha and A. El-Shafie, 2011. Reliability analysis of earth slopes using hybrid chaotic particle swarm optimization. J. Cent. South Univ. Technol., 18(5): 1626-1637. Khajehzadeh, M., M.R. Taha and A. El-shafie, A. 2010. Economic Design of Retaining Wall Using Particle Swarm Optimization with Passive Congregation. Aust. J. Basic Appl. Sci., 4(11): 5500-5507. Khajehzadeh, M., M.R. Taha, A. El-Shafie and M. Eslami, 2012. Locating the general failure surface of earth slope using particle swarm optimization. Civil Eng. Environ. Syst., 29(1): 41-57. DOI: 10.1080/ 10286608.2012.663356 Kim, H. and J. Park, 2006. Improvement of genetic algorithm using PSO and Euclidean data distance. Int. J. Inf. Technol., 12: 142-148. Kuo, I., 2009. An efficient flow-shop scheduling algorithm based on a hybrid particle swarm optimization model. Exp. Syst. Appl., 36: 7027-7032. Kuo, R. and L. Lin, 2010. Application of a hybrid of genetic algorithm and particle swarm optimization algorithm for order clustering. Decis. Support Syst., 49: 451-462. Li, X., 2004. Adaptively choosing neighbourhood bests using species in a particle swarm optimizer for multimodal function optimization. Proceedings of the Congress on Genetic and Evolutionary Computation, pp: 105-116. Liu, B., L. Wang, Y.H. Jin, F. Tang and D.X. Huang, 2005. Improved particle swarm optimization combined with chaos. Chaos Solitons Frac., 25: 1261-1271. Liu, H., A. Abraham and W. Zhang, 2007a. A fuzzy adaptive turbulent particle swarm optimisation. Int. J. Innov. Comput. Appl., 1: 39-47. Liu, H., Z. Cai and Y. Wang, 2010. Hybridizing particle swarm optimization with differential evolution for constrained numerical and engineering optimization. Appl. Soft Comput., 10: 629-640. Liu, Y., Z. Qin, Z. Shi and J. Lu, 2007b. Center particle swarm optimization. Neurocomputing, 70: 672-679. Lovbjerg, M., 2002. Improving particle swarm optimization by hybridization of stochastic search heuristics and self-organized criticality. Master's Thesis, Department of Computer Science, University of Aarhus. Maxfield, A.C.M. and L. Fogel, 1965. Artificial intelligence through a simulation of evolution. Biophysics and Cybernetics Systems: Proceedings of the Second Cybernetics Sciences. Spartan Books, Washington DC. Mendes, R., J. Kennedy and J. Neves, 2004. The fully informed particle swarm: simpler, maybe better. IEEE Trans. Evolut. Comput., 8: 204-210. Mo, W., S. Guan and S. Puthusserypady, 2007. A novel hybrid algorithm for function optimization: particle swarm assisted incremental evolution strategy. Stud. Comput. Intell., 75: 101-125. Mohais, A., R. Mendes, C. Ward and C. Posthoff, 2005. Neighborhood re-structuring in particle swarm optimization. Lect. Notes Comput. Sci., 3809: 776-785. Mohais, A.S., C. Ward and C. Posthoff, 2004. Randomized directed neighborhoods with edge migration in particle swarm optimization. Congress on Evolutionary Computation, pp: 548-555. Momoh, J.A., R. Adapa and M. El-Hawary, 1999a. A review of selected optimal power flow literature to 1993. I. Nonlinear and quadratic programming approaches. IEEE Trans. Power Syst., 14: 96-104. Momoh, J.A., M. El-Hawary and R. Adapa, 1999b. A review of selected optimal power flow literature to 1993. II. Newton, linear programming and interior point methods. IEEE Trans. Power Syst., 14: 105-111. Omran, M.G.H., P. Engelbrecht and A. Salman, 2009. Bare bones differential evolution. Eur. J. Oper. Res., 196: 128-139. 1195 Res. J. Appl. Sci. Eng. Technol., 4(9): 1181-1197, 2012 Padhye, N., 2008. Topology optimization of compliant mechanism using multi-objective particle swarm optimization. Proceedings of the Conference Companion on Genetic and Evolutionary Eomputation, New York, pp: 1831-1834. Pandi, V.R. and B.K. Panigrahi, 2011. Dynamic economic load dispatch using hybrid swarm intelligence based harmony search algorithm. Exp. Syst. Appl., 38: 8509-8851. Pant, M., R. Thangaraj and A. Abraham, 2008. Particle swarm optimization using adaptive mutation. Proceedings of 19th International Conference on Database and Expert Systems Application, Italy, pp: 519-523. Premalatha, K. and A. Natarajan, 2009. Discrete PSO with GA operators for document clustering. Int. J. Recent Trend. Eng., 1: 20-24. Price, K. and R. Storn, 1995. Differential Evolution-a simple and efficient adaptive scheme for global optimization over continuous spaces. International Computer Science Institute-Publications. Ramana, G., M. Arumugam and C. Loo, 2009. Hybrid particle swarm optimization algorithm with fine tuning operators. Int. J. Bio Inspir. Comput., 1: 14-31. Ratnaweera, A., S.K. Halgamuge and H.C. Watson, 2004. Self-organizing hierarchical particle swarm optimizer with time-varying acceleration coefficients. IEEE Trans. Evolut. Comput., 8: 240-255. Robinson, J., S. Sinton and Y. Rahmat-Samii, 2002. Particle swarm, genetic algorithm, and their hybrids: optimization of a profiled corrugated horn antenna. In Proceedings of the IEEE International Symposium in Antennas and Propagation Society, pp: 314-317. Sha, D. and C.Y. Hsu, 2006. A hybrid particle swarm optimization for job shop scheduling problem. Comput. Indust. Eng., 51: 791-808. Shelokar, P., P. Siarry, V. Jayaraman and B. Kulkarni, 2007. Particle swarm and ant colony algorithms hybridized for improved continuous optimization. Applied Math. Comput., 188: 129-142. Shen, Q., W.M. Shi and W. Kong, 2008. Hybrid particle swarm optimization and tabu search approach for selecting genes for tumor classification using gene expression data. Comput. Biol. Chem., 32: 53-60. Shi, Y. and R. Eberhart, 1998. A modified particle swarm optimizer. Evolutionary Computation Proceedings, IEEE World Congress on Computational Intelligence, AK, USA, pp: 69-73. Shi, Y. and R.C. Eberhart, 2001. Fuzzy adaptive particle swarm optimization. In Proceedings Congress on Evolutionary Computation, Seoul, Korea, pp: 101-106 Shunmugalatha, A. and S. Slochanal, 2008. Optimum cost of generation for maximum loadability limit of power system using hybrid particle swarm optimization. Int. J. Electr. Power Energy Syst., 30: 486-490. Song, S., L. Kong, Y. Gan and R. Su, 2008. Hybrid particle swarm cooperative optimization algorithm and its application to MBC in alumina production. Prog. Natural Sci., 18: 1423-1428. Stacey, A., M. Jancic and I. Grundy, 2003. Particle swarm optimization with mutation. The 2003 Congress on Evolutionary Computation, CEC '03., 1422: 1425-1430. Talbi, H. and M. Batouche, 2004. Hybrid particle swarm with differential evolution for multimodal image registration. Proceedings of the IEEE International Conference on Industrial Technology, pp: 1567-1572. Thangaraj, R., M. Pant, A. Abraham and P. Bouvry, 2011. Particle swarm optimization: Hybridization perspectives and experimental illustrations. Applied Math. Comput., 217: 5208-5226 Ting, T., K. Wong and C. Chung, 2008. Hybrid constrained genetic algorithm/particle swarm optimisation load flow algorithm. IET Gener. Trans. Dis., 2: 800-812. Tsou, D. and C. MacNish, 2003. Adaptive particle swarm optimisation for high-dimensional highly convex search spaces. Proceedings of IEEE Congress on Evolutionary Computation 2003 (CEC 2003) Canbella, Australia, pp: 783-789 Tsoulos, I.G. and A. Stavrakoudis, 2010. Enhancing PSO methods for global optimization. Applied Math. Comput., 216: 2988-3001. Valdez, F., P. Melin and O. Castillo, 2010. An improved evolutionary method with fuzzy logic for combining Particle Swarm Optimization and Genetic Algorithms. Applied Soft Comput., 11: 2625-2632. Van den Bergh, F., 2002. An analysis of particle swarm optimizers. Ph.D. Thesis. Department of Computer Science, University of Pretoria, South Africa. van den Bergh, F. and A. Engelbrecht, 2002. A new locally convergent particle swarm optimiser. In Proceedings of the IEEE Conference on Systems, Man, and Cybernetics Hammamet, Tunisia, pp: 1-6. Van den Bergh, F. and A.P. Engelbrecht, 2004. A cooperative approach to particle swarm optimization. IEEE Trans. Evolut. Comput., 8: 225-239. Victoire, T. and A.E. Jeyakumar, 2004. Hybrid PSO-SQP for economic dispatch with valve-point effect. Electr. Power Syst. Res., 71: 51-59. Wang, L., D. Zheng and Q. Lin, 2001. Survey on chaotic optimization methods. Comput. Technol. Automat., 20: 1-5. 1196 Res. J. Appl. Sci. Eng. Technol., 4(9): 1181-1197, 2012 Wang, R. and X. Zhang, 2005. Particle swarm optimization with opposite particles. Advances in Artificial Intelligence, pp: 633-640. Wei, C., Z. He, Y. Zhang and W. Pei, 2002. Swarm directions embedded in fast evolutionary programming. Proceedings of the World Congress on Computational Intelligence, pp: 1278-1283. Xi, M., J. Sun and W. Xu, 2008. An improved quantumbehaved particle swarm optimization algorithm with weighted mean best position. Appl. Math. Comput., 205: 751-759. Xiang, T., X. Liao and K. Wong, 2007. An improved particle swarm optimization algorithm combined with piecewise linear chaotic map. Applied Math. Comput., 190: 1637-1645. Xie, X.F., W.J. Zhang and Z.L. Yang, 2002a. Adaptive particle swarm optimization on individual level. 6th International Conference on Signal Processing, pp: 1215-1218. Xie, X.F., W.J. Zhang and Z.L. Yang, 2002b. Dissipative particle swarm optimization. In Proceedings of the Congress on Evolutionary Computation, pp: 1456-1461. Yang, X., J. Yuan and H. Mao, 2007. A modified particle swarm optimizer with dynamic adaptation. Appl. Math. Comput., 189: 1205-1213. Yao, X., Y. Liu and G. Lin, 1999. Evolutionary programming made faster. IEEE Trans. Evolut. Comput., 3: 82-102. Zahara, E. and Y.T. Kao, 2009. Hybrid Nelder-Mead simplex search and particle swarm optimization for constrained engineering design problems. Expert Syst. Appl., 36: 3880-3886. Zhang, C., J. Ning, S. Lu, D. Ouyang and T. Ding, 2009. A novel hybrid differential evolution and particle swarm optimization algorithm for unconstrained optimization. Operat. Res. Lett., 37: 117-122. Zhang, W.J. and X.F. Xie, 2003. DEPSO: hybrid particle swarm with differential evolution operator. Proceedings of the IEEE International Conference on Systems, Man and Cybernetics, Washington DC, USA, pp: 3816-3821. Zhuang, T., Q. Li, Q. Guo and X. Wang, 2008. A twostage particle swarm optimizer. IEEE World Congress on Computational Intelligence, Hong Kong, pp: 557-563. 1197