The application of the sinc-Galerkin method to an approximate solution of second-order singular Dirichlet-type boundary value problems were discussed in this study. The method is based on approximating functions and their derivatives by using the Whittaker cardinal function. The differential equation is reduced to a system of algebraic equations via new accurate explicit approximations of the inner products without any numerical integration which is needed to solve matrix system. This study shows that the sinc-Galerkin method is a very effective and powerful tool in solving such problems numerically. At the end of the paper, the method was tested on several examples with second-order Dirichlet-type boundary value problems.
Keywords:sinc-Galerkin method; sinc basis functions; Dirichlet-type boundary value problems; LU decomposition method
Sinc methods were introduced by Frank Stenger in  and expanded upon by him in . Sinc functions were first analyzed in  and . An extensive research of sinc methods for two-point boundary value problems can be found in [5,6]. In [7,8], parabolic and hyperbolic problems were discussed in detail. Some kind of singular elliptic problems were solved in , and the symmetric sinc-Galerkin method was introduced in . Sinc domain decomposition was presented in [11-13] and . Iterative methods for symmetric sinc-Galerkin systems were discussed in [15,16] and . Sinc methods were discussed thoroughly in . Applications of sinc methods can also be found in [19,20] and . The article  summarizes the results obtained to date on sinc numerical methods of computation. In , a numerical solution of a Volterra integro-differential equation by means of the sinc collocation method was considered. The paper  illustrates the application of a sinc-Galerkin method to an approximate solution of linear and nonlinear second-order ordinary differential equations, and to an approximate solution of some linear elliptic and parabolic partial differential equations in the plane. The fully sinc-Galerkin method was developed for a family of complex-valued partial differential equations with time-dependent boundary conditions . Some novel procedures of using sinc methods to compute solutions to three types of medical problems were illustrated in , and sinc-based algorithm was used to solve a nonlinear set of partial differential equations in . A new sinc-Galerkin method was developed for approximating the solution of convection diffusion equations with mixed boundary conditions on half-infinite intervals in . The work which was presented in  deals with the sinc-Galerkin method for solving nonlinear fourth-order differential equations with homogeneous and nonhomogeneous boundary conditions. In , sinc methods were used to solve second-order ordinary differential equations with homogeneous Dirichlet-type boundary conditions.
2 Sinc functions preliminaries
In general, approximations can be constructed for infinite, semi-infinite and finite intervals. Define the function
This is shown in Figure 3.
Figure 3. The relationship between the eye-shaped domainand the infinite strip.
For the sinc-Galerkin method, the basis functions are derived from the composite translated sinc functions
for . These are shown in Figure 4 for real values x. The function is an inverse mapping of . We may define the range of on the real line as
Figure 4. Three adjacent memberswhenandof the mapped sinc basis on the interval.
Table 1. Conformal mappings and nodes for some subintervals ofR
Definition 2.1 Let be a simply connected domain in the complex plane C, and let denote the boundary of . Let a, b be points on and ϕ be a conformal map onto such that and . If the inverse map of ϕ is denoted by φ, define
The proof of following theorems can be found in .
For the sinc-Galerkin method, the infinite quadrature rule must be truncated to a finite sum. The following theorem indicates the conditions under which an exponential convergence results.
Theorem 2.2If there exist positive constantsα, βandCsuch that
then the error bound for the quadrature rule (2.14) is
The infinite sum in (2.14) is truncated with the use of (2.16) to arrive at the inequality (2.17). Making the selections
We used Theorems 2.1 and 2.2 to approximate the integrals that arise in the formulation of the discrete systems corresponding to a second-order boundary value problem.
3 The sinc-Galerkin method for singular Dirichlet-type boundary value problems
Consider the following problem:
with Dirichlet-type boundary condition
where P, Q and F are analytic on D. We consider sinc approximation by the formula
The unknown coefficients in Eq. (3.3) are determined by orthogonalizing the residual with respect to the sinc basis functions. The Galerkin method enables us to determine the coefficients by solving the linear system of equations
where w is the weight function. For the second-order problems, it is convenient to take .
For Eq. (3.1), we use the notations (2.21)-(2.23) together with the inner product that, given (3.5) , showed to get the following approximation formulas:
where . If we choose and as given in  the accuracy for each equation between (3.8)-(3.11) will be .
With these notations, the discrete system of equations in (3.5) takes the form:
Three examples were given in order to illustrate the performance of the sinc-Galerkin method to solve a singular Dirichlet-type boundary value problem in this section. The discrete sinc system defined by (3.18) was used to compute the coefficients ; for each example. All of the computations were done by an algorithm which we have developed for the sinc-Galerkin method. The algorithm automatically compares the sinc-method with the exact solutions. It is shown in Tables 2-4 and Figures 5-7 that the sinc-Galerkin method is a very efficient and powerful tool to solve singular Dirichlet-type boundary value problems.
Figure 5. Approximation to the exact solution: the red colored curve displays the exact solution and the green one is the approximate solution of Eq. (4.1).
Figure 6. Approximation to the exact solution: the red colored curve displays the exact solution and the green one is the approximate solution of Eq. (4.2).
Figure 7. Approximation to the exact solution: the red colored curve displays the exact solution and the green one is the approximate solution of Eq. (4.3).
Table 2. The numerical results for the approximate solutions obtained by sinc-Galerkin in comparison with the exact solutions of Eq. (4.1) for
Table 3. The numerical results for the approximate solutions obtained by sinc-Galerkin in comparison with the exact solutions of Eq. (4.2) for
Table 4. The numerical results for the approximate solutions obtained by sinc-Galerkin in comparison with the exact solutions of Eq. (4.3) for
The exact solution of (4.1) is
The problem has an exact solution like
The sinc-Galerkin method was employed to find the solutions of second-order Dirichlet-type boundary value problems on some closed real interval. The main purpose was to find the solution of boundary value problems which arise from the singular problems. The examples show that the accuracy improves with increasing number of sinc grid points N. We have also developed a very efficient and rapid algorithm to solve second-order Dirichlet-type BVPs with the sinc-Galerkin method on the Maple computer algebra system. All of the above computations and graphical representations were prepared by using Maple.
We give the Maple code in the Appendix section.
Appendix: Maple code which we developed for the sinc-Galerkin approximation
The authors declare that they have no competing interests.
AS proposed main idea of the solution schema by using Sinc Method for linear BVPs. He developed computer algorithm and worked on theoretical aspect of problem. MK searched the materials about study and compared with other techniques, contributed with his experience on Nonlinear Approximation methods.
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