[1] R. Weinstock, Calculus of Variations: With Applications to Physics and Engineer-ing, Dover, 1974.
[2] B. Horn and B. Schunck, Determining optical flow, Artificial Intelligence, 17 (1981), 185–203.
[3] K. Ikeuchi and B. Horn, Numerical shape from shading and occluding boundaries,Artificial Intelligence,17(1981),141–184.
[4] L. Elsgolts, Differential Equations and Calculus of Variations, Mir: Moscow, 1977 (translated from the Russian by G. Yankovsky).
[5] I.M. Gelfand and S.V. Fomin, Calculus of Variations, Prentice-Hall: Englewood Cliffs, NJ, 1963.
[6] C.F. Chen and C.H. Hsiao, it A walsh series direct method for solving variational problems, J. Franklin Inst., 300 (1975), 265–280.
[7] R.Y. Chang and M.L. Wang, Shifted Legendre direct method for variational prob-lems, J. Optim. Theory Appl., 39 (1983), 299–306.
[8] . I.R. Horng and J.H. Chou, Shifted Chebyshev direct method for solving variational problems, Internat. J. Systems Sci.,
16 (1985), 855–861.
[9] C. Hwang and Y.P. Shih, Laguerre series direct method for variational problems,J. Optim. Theory Appl.,39(1983),143–149.
[10] S. Dixit, V.K. Singh, A.K. Singh and O.P. Singh, Bernstein Direct Method for Solving Variational Problems, International Mathematical Forum, 5 (2010), 2351–2370.
[11] M. Razzaghi and S. Yousefi,Legendre wavelets direct method for variational prob-lems, Mathematics and Computers in Simulation, 53 (2000), 185–192.
[12] M. Tatari and M. Dehghan, The numerical solution of problems in calculus of variation using Chebyshev finite difference method, Physics Letters A 372 (2008),4037–4040.
[13] J.H. Ahlberg, E.N. Nilson and J.L. Walsh, The Theory of Splines and Their Ap-plications, Academic Press: New York 1967.
[14] T.N.E. Greville, Introduction to spline functions, in: Theory and Application of Spline Functions, Academic Press: New York 1969.
[15] P.M. Prenter, Splines and Variational Methods, John Wiley & Sons INC. 1975.
[16] G. Micula and Sanda Micula, Hand Book of Splines, Kluwer Academic Publisher’s 1999.
[17] S.S. Siddiqi and G. Akram, Numerical solution of a system of fourth order bound-ary value problems using cubic non polynomial spline method, Applied Mathemat-ics and Computation, 190 (2007), 652–661.
[18] M.A. Ramadan, I.F. Lashien and W.K. Zahra, Polynomial and nonpolynomial spline approaches to the numerical solution of second order boundary value prob-lems, Applied Mathematics and Computation, 184 (2007), 476-484.
[19] A. Khan, Parametric cubic spline solution of two point boundary value problems, Applied Mathematics and Computation, 154 (2004), 175–182.
[20] A. Khan and T. Aziz, Parametric cubic spline approach to the solution of a system of second-order boundary-value problems, Journal of Optimization Theory and Applications, 118 (2003), 45–54.
[21] J. Rashidinia, R. Jalilian and R. Mohammadi, Non-polynomial spline methods for the solution of a system of obstacle problems, Applied Mathematics and Compu-tation, 188 (2007) 1984–1990.
[22] J. Rashidinia, R. Jalilian and R. Mohammadi, Convergence analysis of spline solution of certain two-point boundary value problems, Computer Science and En-gineering and Electrical Engineering,16 (2009), 128–136.
[23] M. Zarebnia and N. Aliniya , Sinc-Galerkin method for the solution of problems in calculus of variations, International Journal of Engineering and Natural Sciences,5 (2011), 140–145.