He’s Homotopy Perturbation Method for solving Linear and Non-Linear Fredholm Integro-Differential Equations

In this paper, linear and non-linear Fredholm Integro-Differential Equations with initial conditions are presented. Aiming to find out an analytic and approximate solutions to linear and non-linear Fredholm Integro-Differential Equations, this paper presents a comparative study of He’s Homotopy perturbation method with other traditional methods namely the Variational iteration method (VIM), the Adomian decomposition method (ADM), the Series solution method (SSM) and the Direct computation method (DCM). Comparison of the applied methods of analytic solutions reveals that He’s Homotopy perturbation method is tremendously powerful and effective mathematical tool.


Introduction
Many researchers and scientists studied the integrodifferential equations through their work in science applications like heat transformer, neutron diffusion, and biological species coexisting together with increasing and decreasing rates of generating and diffusion process in general. These kinds of equations can also be found in physics, biology and engineering applications, as well as in models dealing with advanced integral equations such as [1][2], [22][23]. A new perturbation method called Homotopy perturbation method (HPM) was proposed in [8][9][10][11][12][13][14][15][16][17][18][19] by He in 1997, and a systematical description was given in 2000 which is in fact, a coupling of the traditional perturbation method and Homotopy in topology. This new method was further developed and improved by He and applied to various linear and non-linear problems.
Where is the n-th derivative of the unknown function that will be determined, , is the kernel of the integral equation, is a known analytic function, and are linear and nonlinear functions of respectively. For = 0 the equation (1) turn out to be a classical Fredholm integro-differential equation. The Fredholm integrodifferential equations (1) arise from the mathematical modeling of the spatiotemporal development of an epidemic model in addition to various physical and biological models and also from many other scientific phenomena. Nonlinear phenomena, which appear in many applications in scientific fields, such as fluid dynamics, solid state physics, plasma physics, mathematical biology and chemical kinetics, can be modeled by partial differential equations and by integral equations as well. This paper shows a comparative study between He's Homotopy perturbation method [8][9][10][11][12][13][14][15][16][17][18][19] and four traditional methods for analytic treatments of linear and nonlinear integro-differential equations. He's Homotopy perturbation method, well-addressed in [8][9][10][11][12][13][14][15][16][17][18][19] has a constructive attraction that provides the exact solution by computing only a few iterations, mostly two iterations, of the solution series. In addition, He's technique may give the exact Non-Linear Fredholm Integro-Differential Equations solution for linear and nonlinear equations without any need for the so-called He's polynomials. Also this paper, will only focus on a brief discussion of He's Homotopy perturbation method because the details of the method are found in [8][9][10][11][12][13][14][15][16][17][18][19], and in many related works. For the sake of self-sufficiency of the article, the variational iteration method [7,[18][19][20][21], the Adomian decomposition method [5][6], the direct computation method (DCM) [3] and the series solution method [4] are reminded and employed for the comparison goal.

Materials and Methods
Homotopy perturbation method, Variational iteration method, Adomian decomposition method, series solution method, and Direct computation method have been applied to analyze the behavior of the solution of fredholm integrodifferential equations. Finally a comparative study has been made among these methods.

Basic Idea of He's Homotopy Perturbation Method
The Homotopy perturbation method (HPM) proposed by Shijun Liao in 1992 is based on the concept of the Homotopy, a fundamental concept in topology and differential geometry. Consider the nonlinear differential equation, With boundary conditions, " # , Where, ∈ Ω, * ∈ -0,1. is an embedding parameter and is an initial approximation, which satisfies the boundary conditions. Clearly 0 ), 0 = ) − = 0, 0 ), 1 = ) + ) − = 0 As p changes from 0 to 1, Then v(r, p) changes from to . This is called a deformation and ) − , ) + ) − are said to be Homotopy in topology. According to the Homotopy perturbation method, the embedding parameter p can be used as a small parameter and assume that the solution of equation (3) and (4) can be expressed as a power series p, that is ) = ) + *) + * 1 ) 1 + … … … For p=1, the approximate solution of equation (1) therefore, can be expressed as ) = lim 6→ ) = ) + ) + ) 1 + … … … The series in equation (6) is convergent in most cases and the convergence rate of the series depends on the nonlinear operator [Biazar and Ghazvini, 2009;. Moreover, the following judgments are made by He ( , 2006 1. The second order derivative of ) with respect to ) must be small as the parameter may be reasonably large, that is, * → 1 2. 7 8 # $9 $: &7 Must be smaller than one, so that, the series converges

Variational Iteration Method
We consider the general n-th order integro-differential equations of the type [24] ; + ; With initial conditions ; @ =∝ , ; C @ =∝ , … … , ; 8 @ =∝ 8 , Where ∝ D , E = 0,1, … … , − 1, are real constants, m and n are integer and F < . In equation (7) the function f, g and k are given and y is the solution to be determined. Assume that the equation (7) has the unique solution. Here, change the problem to a system of ordinary integro-differential equations and apply the variational iteration to solve it, so that the Lagrange multiplier can be effectively identified.
Rewrite the integro-differential equation (7) as the system of ordinary integro-differential equations With initial conditions ; ∝ =∝ , ; 1 @ =∝ , ; K @ =∝ 1 , … . , ; @ =∝ 8 To illustrate the basic concepts of the variational iteration method, consider the following differential equation Where L is a linear operator, N is a nonlinear operator and g(x) is given continuous function. The basic character of the method is to construct a correction functional for the system, which reads Where S is a general Lagrange multiplier which can be identified optimally via variational theory, it is useful to summarize the Lagrange multipliers as is the n-th approximate solution, and T denotes a restricted variation i.e, X T = 0. According to the variational iteration method, to solve the system (7) Where the superscript (k) is the number of iterations steps. Calculating variation with respect to ; Y ^= 1, 2, 3, … , respectively, and noting that X; Y = 0, We have For arbitrary X; Y ,^= 1, 2, … . , , the following stationary conditions are obtained: And the natural boundary condition 1 + S Y , = 0,^= 1, 2, … , .

The Adomian Decomposition Method
The principal of the ADM when applied to a general nonlinear equation in the following form Invers operator L, with 8 . = .
I , equation (14) can be written as, The decomposition method represents the solution of equation (15) as the following infinite series The nonlinear operator Nu=q is decomposed as = ∑ r p d Where r are Adomian polynomial which are defined as, Substituting equation (16) and (17) Consequently, it can be written as

The Series Solution Method
Assuming that u(x) is an analytic function, it can be represented by a series given by Where @ are constants that will be determined recursively. The first few coefficients can be determined by using the prescribed initial conditions where we may use @ = 0 , @ = C 0 , @ 1 = 1 2! CC 0 , ….
Substituting (20) into both sides of (7), and assuming that the kernel v , is separable as v , = ? ℎ ), obtain ∑ a y p yd

The Direct Computation Method
Assume a standard form to the fredholm integro-differential equation given by Where indicates the n-th derivative of u(x) with respect to x and are constants that define the initial conditions. This yield, It can easily observe that the definite integral in the integro-differential equation (18) involves an integrand that completely depends on the variable t, and therefore, it seems reasonable to set that definite integral in the right side of (23) to a constant α, that is we set ∝= ℎ .
It remains to determine the constant n to evaluate the exact solution .
To find α, we should derive a form for by using (25), followed by substituting this form in (24). To achieve this we integrate both sides of (25) n times from 0 to x, and by using the given initial conditions 0 = , 0 ≤ ≤ -1 Obtain an expression for given by = * ; ∝ , Where * ; n is the result derived from integrating (25) and by using the given initial conditions. Substituting (26) into the right hand side of (24), integrating and solving the resulting equation lead to a complete determination of α. The exact solution of (22) follows immediately upon substituting the resulting value of α into (26).

Solving the Following Linear Fredholm Integro-Differential Equation by Different Methods
Example: Consider the Fredholm Integro-Differential equation  With the effective initial approximation for ) from the conditions (32) and solution of (29), (30), (31) can be written as follows ) = "E ,

Using He's Homotopy Perturbation Method
and so on.

Using Variational Iteration Method
In the view of variations iteration method, construct a correction functional for this equation (27) is given by, Where S is a Lagrange multiplier, therefore Now, the following variational iteration formula can be obtained Q = − gives the exact solution = "E .

Using Adomian Decomposition Method
From (27) Applying the three-fold integral operator 8 defined by, To both sides of (37), that is integrating both sides of (37) thrice from 0 €
This gives approximate solution.

Using the Direct Computation Method
We first set n = CC • J So that given equation (27) can be written as Integrating three times both sides of equation (42)

Using Variation Iteration Method
The correction functional for this equation (45)  and so on. This gives the exact solution by = "E − 0.0349559478 1 . I To both sides of (52), that is integrating both sides of (52) from0 € , and using the given initial condition, which gives = "E − @ + @ + @ 1 1 + @ K K + @ P P + @ Ž Ž + ⋯ gives the series solution, u x = Sinx − 2.43997x 1 .

Conclusion
This paper shows He's Homotopy perturbation method of solving linear and non-linear Fredholm Integro-Differential Equation and conducted a comparative study between He's Homotopy perturbation method and the traditional methods that is Variational iteration method, Adomian decomposition method, Series solution method and Direct computation method. The main advantage of the He's Homotopy perturbation method are the fact that it provides its user with an analytical approximation, in many cases an exact solution in rapidly convergent sequence with elegantly computed terms. Also this method handles linear and non-linear equations in a straightforward manner. The four traditional methods suffer from the tedious work of calculation. Other traditional methods, that is usually used to solve integro-differential equations analytically and numerically, were not examined in this work, due to the huge size of calculations needed by these methods. Generally speaking, He's Homotopy perturbation method is convenient and more efficient compared to other techniques.