Solving Delay Differential Equations by an Accurate Method with Interpolation

and Applied Analysis 3


Introduction
In this paper we consider delay differential equations in the reproducing kernel space: 1 ( ) ( ( )) + 1 ( ) (ℎ ( )) + 1 ( ) ( ( )) = ( ) , 0 < < 1, where ( ) ∈ 3 2 [0, 1] and ( ) ∈ 1 2 [0, 1]. The theory of reproducing kernels [1] was used for the first time at the beginning of the 20th century by S. Zaremba in his work on boundary value problems for harmonic and biharmonic functions. In recent years, a lot of attention has been devoted to the study of RKM to investigate various scientific models. The RKM which accurately computes the series solution is of great interest to applied sciences. The method provides the solution in a rapidly convergent series with components that can be elegantly computed. The book [2] provides excellent overviews of the existing reproducing kernel methods for solving various model problems such as integral and integrodifferential equations.
The efficiency of the method was used by many authors to investigate several scientific applications. Geng and Cui [3] applied the RKM to handle the second-order boundary value problems. Wang et al. [4] investigated a class of singular boundary value problems by this method and the obtained results were good. Zhou et al. [5] used the RKM effectively to solve second-order boundary value problems. In [6], the method was used to solve nonlinear infinite-delaydifferential equations. Wang and Chao [7] and Zhou and Cui [8] independently employed the RKM to variable-coefficient partial differential equations. Geng and Cui [9] and Du and Cui [10] researched the approximate solution of the forced Duffing equation with integral boundary conditions by combining the homotopy perturbation method and the RKM. Wu and Li [11] applied iterative reproducing kernel method to obtain the analytical approximate solution of a nonlinear oscillator with discontinuities. Yang et al. [12] used this method for solving the system of the linear Volterra integral equations with variable coefficients. A particular singular integral equation was solved by Du and Shen [13]. Barbieri and Meo [14] have studied evaluation of the integral terms in reproducing kernel methods. Third-order threepoint boundary value problems were considered by Wu and Li [15]. Chen and Chen [16] investigated the exact solution of system of linear operator equations in reproducing kernel spaces. Akgül has investigated fractional order boundary value problems by RKM [17]. Inc et al. have solved ordinary and partial differential equations by RKM [18][19][20].
The paper is organized as follows. Section 2 introduces several reproducing kernel spaces. The associated linear operator is presented in Section 3. Section 4 provides the main results. The exact and approximate solutions of problems and an iterative method are developed in the reproducing kernel space in this section. We have proved that the approximate solutions converge to the exact solutions uniformly. Some numerical experiments are illustrated in Section 5. Some conclusions are given in Section 6.

Reproducing Kernel Spaces.
In this section, we define some useful reproducing kernel spaces. The last condition is called "the reproducing property" as the value of the function at the point is reproduced by the inner product of with (⋅, ).
The third derivative of exists almost everywhere since is absolutely continuous. The inner product and the norm in The space 3 2 [0, 1] is called a reproducing kernel space, as, for each fixed ∈ [0, 1] and any ∈ 3 2 [0, 1], there exists a function such that Definition 3. We define the space 1 The inner product and the norm in 1 2 [0, 1] are defined by The space 1 2 [0, 1] is a reproducing kernel space, and its reproducing kernel function is given by Cui and Lin [2]: Lemma 4 (see [21]). The space 3 2 [0, 1] is a reproducing kernel space, and its reproducing kernel function is given by where ( ) and ( ) coefficients can be found by Maple 16.

Solution Representation in 3 2 [0, 1]
In this section, the solution of (1) is considered in the reproducing kernel space 3 2 [0, 1]. On defining the linear operator : 3 model problem (1) takes the form In (9), since V( ) is sufficiently smooth, we see that : is a bounded linear operator. For convenience, we write instead of V in (10). (9) is a bounded linear operator.

Theorem 5. The linear operator defined by
Proof. We only need to prove ‖ ‖ 2 , where > 0 is a positive constant. By (6), we have By reproducing property, we have Abstract and Applied Analysis where 1 > 0 is a positive constant; thus, Since we have where 2 > 0 is a positive constant, so we have that is where = 2 1 + 2 2 > 0 is a positive constant. This completes the proof.

The Structure of the Solution and the Main Results
From (9), it is clear that : The subscript by the operator indicates that the operator applies to the function of . Clearly, ( ) ∈ 3 2 [0, 1]. where Proof. From (19) and uniqueness of solution of (10), we have This completes the proof.

Interpolation for Reproducing Kernel Method.
We used interpolation to find the numerical results by RKM with where 0.1 ≤ < < < ≤ 1. More details for interpolation can be found in [24].

Numerical Results
In this section, four numerical examples are provided to show the accuracy of the present method. We used interpolation for Examples 12-14. The RKM does not require discretization of the variables, that is, time and space; it is not effected by computation round-off errors and one is not faced with necessity of large computer memory and time. The accuracy of the RKM for the delay differential equation is controllable and absolute errors are small with present choice of (see Tables 1-6). The numerical results we obtained justify the advantage of this methodology.
Abstract and Applied Analysis 5 Thus, if the method described above is applied, then we find Table 1.
Example 13. We take notice of equation We use transformation to obtain Thus, if the method described above is applied, then we find Table 2.
Example 14. We regard the following equation: We use transformation Thus, if the method described above is applied, then we find Table 3.
The exact solution of (45) is given as Thus, if the method described above is applied, then we find Tables 4, 5, and 6.

Conclusion
In this paper, we introduced an algorithm for finding approximate solutions of delay differential equations with RKM. For illustration purposes, four examples were selected to show the computational accuracy. It may be concluded that the RKM is very powerful and efficient in finding approximate solutions for wide classes of problems. Solutions obtained by the present method are uniformly convergent. As shown in Tables 1-6, results of numerical examples show that the present method is an accurate and reliable analytical method for these problems. The present study has confirmed that the RKM offers significant advantages in terms of its straightforward applicability, its computational effectiveness, and its accuracy to solve the strongly nonlinear equations.