Hindawi Publishing Corporation Advances in Difference Equations Volume 2010, Article ID 841643, 11 pages doi:10.1155/2010/841643 Research Article Approximation of Solution of Some m-Point Boundary Value Problems on Time Scales Rahmat Ali Khan1 and Mohammad Rafique2 1 Centre for Advanced Mathematics and Physics, National University of Sciences and Technology (NUST), H-12, Islamabad 46000, Pakistan 2 Department of Basic Sciences, College of Electrical and Mechanical Engineering, National University of Sciences and Technology (NUST), Peshawar Road, Rawalpindi 46000, Pakistan Correspondence should be addressed to Mohammad Rafique, mrdhillon@yahoo.com Received 24 August 2009; Revised 13 May 2010; Accepted 2 June 2010 Academic Editor: Ondřej Došlý Copyright q 2010 R. A. Khan and M. Rafique. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The method of upper and lower solutions and the generalized quasilinearization technique for second-order nonlinear m-point dynamic equations on time scales of the type xΔΔ t ft, xσ , m−1 t ∈ 0, 1T 0, 1 ∩ T, x0 0, xσ 2 1 m−1 i1 αi xηi , ηi ∈ 0, 1T , i1 αi ≤ 1, are developed. A monotone sequence of solutions of linear problems converging uniformly and quadratically to a solution of the problem is obtained. 1. Introduction Many dynamical processes contain both continuous and discrete elements simultaneously. Thus, traditional mathematical modeling techniques, such as differential equations or difference equations, provide a limited understanding of these types of models. A simple example of this hybrid continuous-discrete behavior appears in many natural populations: for example, insects that lay their eggs at the end of the season just before the generation dies out, with the eggs laying dormant, hatching at the start of the next season giving rise to a new generation. For more examples of species which follow this type of behavior, we refer the readers to 1. Hilger 2 introduced the notion of time scales in order to unify the theory of continuous and discrete calculus. The field of dynamical equations on time scales contain, links and extends the classical theory of differential and difference equations, besides many others. There are more time scales than just R corresponding to the continuous case and N corresponding to the discrete case and hence many more classes of dynamic equations. An excellent resource with an extensive bibliography on time scales was produced by Bohner and Peterson 3, 4. 2 Advances in Difference Equations Recently, existence theory for positive solutions of boundary value problems BVPs on time scales has attracted the attention of many authors; see, for example, 5–12 and the references therein for the existence theory of some two-point BVPs, and 13–16 for threepoint BVPs on time scales. For the existence of solutions of m-point BVPs on time scales, we refer the readers to 17. However, the method of upper and lower solutions and the quasilinearization technique for BVPs on time scales are still in the developing stage and few papers are devoted to the results on upper and lower solutions technique and the method of quasilinearization on time scales 18–21. The pioneering paper on multipoint BVPs on time scales has been the one in 21 where lower and upper solutions were combined with degree theory to obtain very wide-ranging existence results. Further, the authors of 21 studied existence results for more general three-point boundary conditions which involve first delta derivatives and they also developed some compatibility conditions. We are very grateful to the reviewer for directing us towards this important work. Recently, existence results via upper and lower solutions method and approximation of solutions via generalized quasilinearization method for some three-point boundary value problems on time scales have been studied in 16. Motivated by the work in 16, 17, in this paper, we extend the results studied in 16 to a class of m-point BVPs of the type xΔΔ t ft, xσ t, t ∈ 0, 1T , m−1 x0 0, x σ 2 1 αi x ηi , 1.1 i1 where ηi ∈ 0, 1T , m−1 i1 αi ≤ 1, and t is from a so-called time scale T which is an arbitrary closed subset of R. Existence of at least one solution for 1.1 has already been studied in 17 by the Krasnosel’skii and Zabreiko fixed point theorems. We obtain existence and uniqueness results and develop a method to approximate the solutions. Assume that T has a topology that it inherits from the standard topology on R and define the time scale interval 0, 1T {t ∈ T : 0 ≤ t ≤ 1}. For t ∈ T, define the forward jump operator σ : T → T by σt inf{s ∈ T : s > t} and the backward jump operator ρ : T → T by ρt sup{s ∈ T : s < t}. If σt > t, t is said to be right scattered, and if σt t, t is said to be right dense. If ρt < t, t is said to be left scattered, and if ρt t, t is said to be left dense. A function f : T → R is said to be rd-continuous provided it is continuous at all rightdense points of T and its left-sided limit exists at left-dense points of T. A function f : T → R is said to be ld-continuous provided it is continuous at all left-dense points of T and its rightsided limit exists at right-dense points of T. Define Tk T − {m} if T has a left-scattered maximum at m; otherwise Tk T. For f : T → R and t ∈ Tk , the delta derivative f Δ t of f at t if exists is defined by the following Given that > 0, there exists a neighborhood U of t such that 1.2 f σt − fs − f Δ tσt − s ≤ |σt − s|, ∀s ∈ U. If there exists a function F : T → R such that F Δ t ft for all t ∈ T, F is said to be the delta antiderivative of f and the delta integral is defined by b a fτΔτ Fb − Fa, a, b ∈ T. 1.3 Advances in Difference Equations 3 2 0, σ 2 1T to be the set of all functions y : T → R such that Definition 1.1. Define Crd 2 Crd 0, σ 2 1 T y : y, yΔ ∈ C 0, σ 2 1 and yΔΔ ∈ Crd 0, 1T . T 1.4 2 A solution of 1.1 is a function y ∈ Crd 0, σ 2 1T which satisfies 1.1 for each t ∈ 0, 1T . Let us denote Crd 0, 1T × R yt, x : y·, x is Crd 0, 1T for every x ∈ R and yt, · is continuous on R uniformly at each t ∈ 0, 1T , 2 Crd 0, 1T × R yt, x : y·, x, yx ·, x, yx ·, x are Crd 0, 1T 1.5 for every x ∈ R and yt, ·, yx t, ·, yxx t, · are continuous on R uniformly at each t ∈ 0, 1T . The purpose of this paper is to develop the method of upper and lower solutions and the method of quasilinearization 22–26. Under suitable conditions on f, we obtain a monotone sequence of solutions of linear problems. We show that the sequence of approximants converges uniformly and quadratically to a unique solution of the problem. 2. Upper and Lower Solutions Method We write the BVP 1.1 as an equivalent Δ-integral equation xt σb Gt, sfs, xσ sΔs, a 2.1 t ∈ 0, σ 2 1T , where Gt, s is a Green’s function for the problem yΔΔ t , y0 0, t ∈ 0, 1T , 2.2 m−1 y σ 2 1 − αi x ηi 0, i1 and it is given by 17 Gt, s ⎧ k ⎪ 1 ⎪ ⎪ , t ≤ s, σ ηk ≤ s ≤ ηk1 , αi σ ηi − σs − σsα t 1 ⎪ ⎪ ⎪ T i1 ⎨ ⎪ ⎪ k ⎪ t ⎪ ⎪ ⎪ αi σ ηi − σs − σsα , ⎩σs T i1 where k 0, 1, 2, . . . , m − 1, η0 0, and ηk1 σ 2 1. σs ≤ t, σ ηk ≤ s ≤ ηk1 , 2.3 4 Advances in Difference Equations Notice that Gt, s > 0 on 0, σ 2 1T × 0, σ1T and is rd-continuous. Define an operator N : C0, σ 2 1T → C0, σ 2 1T by Nxt σ1 Gt, sfs, xσ sΔs, 0 t ∈ 0, σ 2 1T . 2.4 By a solution of 2.1, we mean a solution of the operator equation I − Nx 0, that is, a fixed point of N, 2.5 where I is the identity. If f ∈ C0, 1T × R and is bounded on 0, 1T × R, then by ArzelaAscoli theorem N is compact and Schauder’s fixed point theorem yields a fixed point of N. We discuss the case when f is not necessarily bounded on 0, σ 2 1T × R. 2 Definition 2.1. We say that α ∈ Crd 0, σ 2 1T is a lower solution of the BVP 1.1, if αΔΔ t ≥ ft, ασ t, α0 ≤ 0, α σ 2 1 ≤ t ∈ 0, 1T , αi α ηi . m−1 2.6 i1 2 0, σ 2 1T is an upper solution of the BVP 1.1 if Similarly, β ∈ Crd βΔΔ t ≤ f t, βσ t , β0 ≥ 0, β σ 2 1 ≥ t ∈ 0, 1T , αi β ηi . m−1 2.7 i1 Theorem 2.2. (comparison result) Assume that α, β are lower and upper solutions of the boundary value problem 1.1. If ft, x ∈ Crd 0, 1T × R and is strictly increasing in x for each t ∈ 0, σ 2 1T , then α ≤ β on 0, σ 2 1T . 2 Proof. Define vt αt − βt, t ∈ 0, σ 2 1T . Then v ∈ Crd 0, σ 2 1T and the BCs imply that m−1 v0 ≤ 0, v σ 2 1 ≤ αi v ηi . 2.8 i1 Assume that the conclusion of the theorem is not true. Then, v has a positive maximum at some t0 ∈ 0, σ 2 1T . Clearly, t0 > 0. If t0 ∈ 0, σ 2 1T , then, the point t0 is not simultaneously left dense and right scattered; see, for example, 12. Hence by Lemma 1 of 12, vΔΔ ρt0 ≤ 0. 2.9 On the other hand, using the definitions of lower and upper solutions, we obtain vΔΔ ρt0 αΔΔ ρt0 − βΔΔ ρt0 ≥ f ρt0 , ασ ρt0 − f ρt0 , βσ ρt0 . 2.10 Advances in Difference Equations 5 Since t0 is not simultaneously left dense and right scattered, it is left scattered and right scattered, left dense and right dense, or left scattered and right dense. In either case σρt0 t0 . Using the increasing property of ft, x in x, we obtain vΔΔ ρt0 > 0, 2.11 a contradiction. Hence vt has no positive local maximum. If t0 σ 2 1, then vσ 2 1 > 0. If any one of the ηi is such that vηi vσ 2 1, then v has a positive local maximum, a contradiction. Hence v ηi < v σ 2 1 , for each i 1, 2, 3, . . . , m − 1. 2.12 Moreover, if αi 0 for each i 1, 2, 3, . . . , m − 1, then, from the BCs m−1 αi v ηi , v σ 2 1 ≤ 2.13 i1 0 for some i 1, 2, 3, . . . , m − 1, and we have vσ 2 1 ≤ 0, a contradiction. Hence, αi / consequently, in view of 2.12 and the BCs, it follows that m−1 m−1 v σ 2 1 ≤ αi v ηi < αi v σ 2 1 . i1 2.14 i1 m−1 2 Hence, 1 − m−1 i1 αi vσ 1 < 0, which leads to i1 αi > 1, a contradiction. 2 2 1. Thus, vt ≤ 0 on 0, σ 1 σ Hence t0 / T. Corollary 2.3. Under the hypotheses of Theorem 2.2, the solutions of the BVP 1.1, if they exist, are unique. The following theorem establishes existence of solutions to the BVP 1.1 in the presence of well-ordered lower and upper solutions. Theorem 2.4. Assume that α, β are lower and upper solutions of the BVP 1.1 such that α ≤ β on 0, σ 2 1T . If ft, x ∈ Crd 0, 1T × R, then the BVP 1.1 has a solution x such that α ≤ x ≤ β, on 0, σ 2 1T . 2.15 The proof essentially is a minor modification of the ideas in 21 and so is omitted. 3. Generalized Approximations Technique We develop the approximation technique and show that, under suitable conditions on f, there exists a bounded monotone sequence of solutions of linear problems that 6 Advances in Difference Equations converges uniformly and quadratically to a solution of the nonlinear original problem. If ∂2 /∂x2 ft, x ∈ C0, 1T × R and is bounded on 0, σ 2 1T × α, β, where α min αt, t ∈ 0, σ 2 1T , β max βt, t ∈ 0, σ 2 1T , 3.1 there always exists a function Φ such that ∂2 ft, x Φt, x ≤ 0, ∂x2 on 0, 1T × α, β , 3.2 2 0, σ 2 1T × R, and it is such that ∂2 /∂x2 Φt, x ≤ 0 on 0, σ 2 1T × α, β. where Φ ∈ Crd For example, let M max{|fxx t, x| : t, x ∈ 0, σ 2 1T × α, β}, then we choose Φ −t − M/2x2 . Clearly, ∂2 ft, x Φt, x ≤ 0, 2 ∂x on 0, σ 2 1T × α, β . 3.3 2 Define F : 0, 1T × R → R by Ft, x ft, x Φt, x. Note that F ∈ Crd 0, σ 2 1T × R and ∂2 Ft, x ≤ 0, ∂x2 on 0, 1T × α, β . 3.4 Theorem 3.1. Assume that A1 α, β are lower and upper solutions of the BVP 1.1 such that α ≤ β on 0, σ 2 1T , 2 A2 f ∈ Crd 0, σ 2 1T × R and f is increasing in x for each t ∈ 0, σ 2 1T . Then, there exists a monotone sequence {wn } of solutions of linear problems converging uniformly and quadratically to a unique solution of the BVP 1.1. Proof. Conditions A1 and A2 ensure the existence of a unique solution x of the BVP 1.1 such that αt ≤ xt ≤ βt, 3.5 t ∈ 0, σ 2 1T . In view of 3.4, we have ft, x ≤ f t, y Fx t, y x − y − Φt, x − Φ t, y , on 0, 1T × α, β . 3.6 The mean value theorem and the fact that Φx is nonincreasing in x on α, β for each t ∈ 0, σ 2 1T yield Φt, x − Φ t, y Φx t, c x − y ≥ Φx t, β x − y , for x ≥ y, 3.7 Advances in Difference Equations 7 where x, y ∈ α, β such that y ≤ c ≤ x. Substituting in 3.6, we have ft, x ≤ f t, y Fx t, y − Φx t, β x−y , for x ≥ y, 3.8 on 0, σ 2 1T × α, β. Define g : 0, σ 2 1T × R2 → R by g t, x, y f t, y Fx t, y − Φx t, β x−y . 3.9 We note that gt, ., . is continuous for each t ∈ 0, 1T and g., x, y is rd-continuous for each x, y ∈ R2 . Moreover, g satisfies the following relations on 0, 1T × α, β: gx t, x, y Fx t, y − Φx t, β ≥ Fx t, y − Φx t, y fx t, y ≥ 0, ft, x ≤ g t, x, y , for x ≥ y, 3.10 3.11 ft, x gt, x, x. Now, we develop the iterative scheme to approximate the solution. As an initial approximation, we choose w0 α and consider the linear problem xΔΔ t g t, xσ t, w0σ t , x0 0, t ∈ 0, 1T , m−1 x σ 2 1 αi x ηi . 3.12 i1 Using 3.11 and the definition of lower and upper solutions, we get g t, w0σ t, w0σ t f t, w0σ t ≤ w0ΔΔ t, t ∈ 0, 1T , g t, βσ t, w0σ t ≥ f t, βσ t ≥ βΔΔ t, t ∈ 0, 1T , 3.13 which imply that w0 and β are lower and upper solutions of 3.12, respectively. Hence by 2 0, σ 2 1T of 3.12 Theorem 2.4 and Corollary 2.3, there exists a unique solution w1 ∈ Crd such that w0 t ≤ w1 t ≤ βt, on 0, σ 2 1 . T 3.14 Using 3.11 and the fact that w1 is a solution of 3.12, we obtain w1ΔΔ t g t, w1σ t, w0σ t ≥ f t, w1σ t , w1 0 0, t ∈ 0, 1T , m−1 αi w1 ηi , w1 σ 2 1 i1 3.15 8 Advances in Difference Equations which implies that w1 is a lower solution of the problem 1.1. Similarly, in view of A1 , 3.11, and 3.15, we can show that w1 and β are lower and upper solutions of the problem xΔΔ t g t, xσ t, w1σ t , x0 0, t ∈ 0, 1T , 3.16 m−1 x σ 2 1 αi x ηi . i1 2 Hence by Theorem 2.4 and Corollary 2.3, there exists a unique solution w2 ∈ Crd 0, σ 2 1T of the problem 3.16 such that w1 t ≤ w2 t ≤ βt, on 0, σ 2 1 . 3.17 T Continuing in the above fashion, we obtain a bounded monotone sequence {wn } of solutions of linear problems satisfying w0 t ≤ w1 t ≤ w2 t ≤ w3 t ≤ · · · ≤ wn t ≤ βt, on 0, σ 2 1T , 3.18 where the element wn of the sequence is a solution of the linear problem σ xΔΔ t g t, xσ t, wn−1 t , x0 0, t ∈ 0, 1T , 3.19 m−1 x σ 2 1 αi x ηi , i1 and is given by wn t σ1 0 σ Gt, sg s, wnσ s, wn−1 s Δs, t ∈ 0, σ 2 1 . T 3.20 By standard arguments as in 19, the sequence converges to a solution of 1.1. Now, we show that the convergence is quadratic. Set vn1 t xt − wn1 t, t ∈ 0, σ 2 1T , where x is a solution of 1.1. Then, vn1 t ≥ 0 on 0, σ 2 1T and the boundary conditions imply that m−1 vn1 0 0, vn1 σ 2 1 αi vn1 ηi . i1 3.21 Advances in Difference Equations 9 Now, in view of the definitions of F and g, we obtain σ vnΔΔ t ft, xσ t − g s, wnσ t, wn−1 t Ft, xσ t − Φt, xσ t σ σ σ − f t, wn−1 wnσ t − wn−1 t Fx t, wn−1 t − Φx t, β t 3.22 σ σ σ Ft, xσ t − F t, wn−1 t − Fx t, wn−1 t wnσ t − wn−1 t σ σ − Φt, xσ t − Φ t, wn−1 t − Φx t, β wnσ t − wn−1 t , t ∈ 0, 1T . Using the mean value theorem repeatedly and the fact that Φxx ≤ 0 on 0, 1T × α, β, we obtain σ σ σ Φt, xσ t − Φ t, wn−1 t ≤ Φx t, wn−1 t xσ t − wn−1 t , σ σ σ Ft, xσ t − F t, wn−1 t − Fx t, wn−1 t wnσ t − wn−1 t Fxx t, ξ σ 2 σ σ σ Fx t, wn−1 x t − wn−1 t xσ t − wn−1 t t 2 σ σ − Fx t, wn−1 t wnσ t − wn−1 t 3.23 2 Fxx t, ξ σ σ σ Fx t, wn−1 x t − wn−1 t xσ t − wnσ t t 2 σ ≥ Fx t, wn−1 t xσ t − wnσ t − dvn−1 2 , σ t ≤ ξ ≤ xσ t, d max{|Fxx t, x|/2 : t, x ∈ 0, σ 2 1T × α, β}, and v where wn−1 max{vt : t ∈ 0, σ 2 1T }. Hence 3.22 can be rewritten as σ vnΔΔ t ≥ Fx t, wn−1 t xσ t − wnσ t − dvn−1 2 σ σ σ − Φx t, wn−1 t xσ t − wn−1 t Φx t, β wnσ t − wn−1 t σ fx t, wn−1 t xσ t − wnσ t − dvn−1 2 σ σ Φx t, β − Φx t, wn−1 t wnσ t − wn−1 t σ σ σ σ fx t, wn−1 t wnσ t − wn−1 t x t − wnσ t − dvn−1 2 Φxx t, ξ1 β − wn−1 σ σ σ σ ≥ fx t, wn−1 t xnσ t − wn−1 t x t − wnσ t − dvn−1 2 Φxx t, ξ1 β − wn−1 σ σ ≥ −dvn−1 2 − d1 β − wn−1 txσ t − wn−1 t, t ∈ 0, 1T , 3.24 10 Advances in Difference Equations σ where wn−1 t ≤ ξ1 ≤ wnσ t, d1 max{|Φxx | : t, x ∈ 0, 1T × α, β}, and we used the fact that fx ≥ 0 on 0, 1T × α, β. Choose r > 1 such that σ β t − wσ t ≤ r xσ t − wσ t, n−1 n−1 on 0, 1T . 3.25 Therefore, we obtain vnΔΔ t ≥ −d2 vn−1 2 , t ∈ 0, 1T , 3.26 where d2 d rd1 . By comparison result, vn t ≤ zt, t ∈ 0, 1T , where zt is the unique solution of the linear BVP zΔΔ t d2 vn−1 2 , t ∈ a, bT , m−1 z0 0, z σ 2 1 αi z ηi . 3.27 i1 Hence, vn t ≤ zt d2 σ1 Gt, svn−1 2 Δs ≤ d3 vn−1 2 , 3.28 0 σ1 where d3 d2 max{ 0 |Gt, s|Δs : t ∈ 0, σ 2 1T }. Taking the maximum over 0, 1T , we obtain vn ≤ d3 vn−1 2 , 3.29 which shows the quadratic convergence. Acknowledgement The authors are thankful to reviewers for their valuable comments and suggestions. References 1 F. B. Christiansen and T. M. Fenchel, “Theories of Populations in Biological Communities, Ecological Studies,” vol. 20, Springer, Berlin, Germany, 1977. 2 S. Hilger, “Analysis on measure chains—a unified approach to continuous and discrete calculus,” Results in Mathematics, vol. 18, no. 1-2, pp. 18–56, 1990. 3 M. Bohner and A. Peterson, Dynamic Equations on Time Scales: An Introduction with Applications, Birkhäuser, Boston, Mass, USA, 2001. 4 M. Bohner and A. Peterson, Eds., Advances in Dynamic Equations on Time Scales, Birkhäuser, Boston, Mass, USA, 2003. 5 R. P. Agarwal and D. O’Regan, “Nonlinear boundary value problems on time scales,” Nonlinear Analysis: Theory, Methods & Applications, vol. 44, no. 4, pp. 527–535, 2001. Advances in Difference Equations 11 6 D. Anderson, R. Avery, and J. Henderson, “Existence of solutions for a one dimensional p-Laplacian on time-scales,” Journal of Difference Equations and Applications, vol. 10, no. 10, pp. 889–896, 2004. 7 F. M. Atici and G. Sh. Guseinov, “On Green’s functions and positive solutions for boundary value problems on time scales,” Journal of Computational and Applied Mathematics, vol. 141, no. 1-2, pp. 75–99, 2002. 8 R. I. Avery and D. R. Anderson, “Existence of three positive solutions to a second-order boundary value problem on a measure chain,” Journal of Computational and Applied Mathematics, vol. 141, no. 1-2, pp. 65–73, 2002. 9 L. Erbe and A. Peterson, “Positive solutions for a nonlinear differential equation on a measure chain,” Mathematical and Computer Modelling, vol. 32, no. 5-6, pp. 571–585, 2000. 10 J. Henderson, “Double solutions of impulsive dynamic boundary value problems on a time scale,” Journal of Difference Equations and Applications, vol. 8, no. 4, pp. 345–356, 2002. 11 J. Henderson, A. Peterson, and C. C. Tisdell, “On the existence and uniqueness of solutions to boundary value problems on time scales,” Advances in Difference Equations, vol. 2004, no. 2, pp. 93–109, 2004. 12 C. C. Tisdell and H. B. Thompson, “On the existence of solutions to boundary value problems on time scales,” Dynamics of Continuous, Discrete & Impulsive Systems. Series A, vol. 12, no. 5, pp. 595–606, 2005. 13 D. R. Anderson and R. I. Avery, “An even-order three-point boundary value problem on time scales,” Journal of Mathematical Analysis and Applications, vol. 291, no. 2, pp. 514–525, 2004. 14 T. G. Bhaskar, “Comparison theorem for a nonlinear boundary value problem on time scales,” Journal of Computational and Applied Mathematics, vol. 141, no. 1-2, pp. 117–122, 2002. 15 E. R. Kaufmann, “Positive solutions of a three-point boundary-value problem on a time scale,” Electronic Journal of Differential Equations, vol. 2003, no. 82, pp. 1–11, 2003. 16 R. A. Khan, J. J. Nieto, and V. Otero-Espinar, “Existence and approximation of solution of three-point boundary value problems on time scales,” Journal of Difference Equations and Applications, vol. 14, no. 7, pp. 723–736, 2008. 17 B. Karna and B. A. Lawrence, “An existence result for a multipoint boundary value problem on a time scale,” Advances in Difference Equations, vol. 2006, Article ID 63208, 8 pages, 2006. 18 E. Akin-Bohner and F. M. Atici, “A quasilinearization approach for two point nonlinear boundary value problems on time scales,” The Rocky Mountain Journal of Mathematics, vol. 35, no. 1, pp. 19–45, 2005. 19 F. M. Atici, P. W. Eloe, and B. Kaymakçalan, “The quasilinearization method for boundary value problems on time scales,” Journal of Mathematical Analysis and Applications, vol. 276, no. 1, pp. 357–372, 2002. 20 F. M. Atici and S. G. Topal, “The generalized quasilinearization method and three point boundary value problems on time scales,” Applied Mathematics Letters, vol. 18, no. 5, pp. 577–585, 2005. 21 A. C. Peterson, Y. N. Raffoul, and C. C. Tisdell, “Three point boundary value problems on time scales,” Journal of Difference Equations and Applications, vol. 10, no. 9, pp. 843–849, 2004. 22 R. E. Bellman and R. E. Kalaba, Quasilinearization and Nonlinear Boundary-Value Problems, vol. 3 of Modern Analytic and Computional Methods in Science and Mathematics, American Elsevier, New York, NY, USA, 1965. 23 R. A. Khan, “Approximations and rapid convergence of solutions of nonlinear three point boundary value problems,” Applied Mathematics and Computation, vol. 186, no. 2, pp. 957–968, 2007. 24 V. Lakshmikantham and A. S. Vatsala, Generalized Quasilinearization for Nonlinear Problems, vol. 440 of Mathematics and Its Applications, Kluwer Academic Publishers, Dordrecht, The Netherlands, 1998. 25 V. Lakshmikantham and A. S. Vatsala, “Generalized quasilinearization versus Newton’s method,” Applied Mathematics and Computation, vol. 164, no. 2, pp. 523–530, 2005. 26 J. J. Nieto, “Generalized quasilinearization method for a second order ordinary differential equation with Dirichlet boundary conditions,” Proceedings of the American Mathematical Society, vol. 125, no. 9, pp. 2599–2604, 1997.