## Existence and Asymptotic Behaviour of Solutions of Differential and Integral Equations in Some Function Spaces

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Eman M. A. Hilal, Tarig M. Elzaki, "Solution of Nonlinear Partial Differential Equations by New Laplace Variational Iteration Method", *Journal of Function Spaces*, vol. 2014, Article ID 790714, 5 pages, 2014. https://doi.org/10.1155/2014/790714

# Solution of Nonlinear Partial Differential Equations by New Laplace Variational Iteration Method

**Academic Editor:**Leszek Olszowy

#### Abstract

The aim of this study is to give a good strategy for solving some linear and nonlinear partial differential equations in engineering and physics fields, by combining Laplace transform and the modified variational iteration method. This method is based on the variational iteration method, Laplace transforms, and convolution integral, introducing an alternative Laplace correction functional and expressing the integral as a convolution. Some examples in physical engineering are provided to illustrate the simplicity and reliability of this method. The solutions of these examples are contingent only on the initial conditions.

#### 1. Introduction

Nonlinear equations are of great importance to our contemporary world. Nonlinear phenomena have important applications in applied mathematics, physics, and issues related to engineering. Despite the importance of obtaining the exact solution of nonlinear partial differential equations in physics and applied mathematics, there is still the daunting problem of finding new methods to discover new exact or approximate solutions.

In the recent years, many authors have devoted their attention to study solutions of nonlinear partial differential equations using various methods. Among these attempts are the Adomian decomposition method, homotopy perturbation method, variational iteration method [1–5], Laplace variational iteration method [6–8], differential transform method, and projected differential transform method.

Many analytical and numerical methods have been proposed to obtain solutions for nonlinear PDEs with fractional derivatives, such as local fractional variational iteration method [9], local fractional Fourier method, Yang-Fourier transform, and Yang-Laplace transform. Two Laplace variational iteration methods are currently suggested by Wu in [10–13].

In this work, we will use the new method termed He’s Laplace variational iteration method, and it will be employed in a straightforward manner.

Also, the main result of this paper is to introduce an alternative Laplace correction functional and express the integral as a convolution. This approach can tackle functions with discontinuities and impulse functions effectively.

#### 2. New Laplace Variational Iteration Method

To illustrate the idea of new Laplace variational iteration method, we consider the following general differential equations in physics: where is a linear partial differential operator given by , is nonlinear operator, and is a known analytical function.

According to the variational iteration method, we can construct a correction function for (1) as follows: where is a general Lagrange multiplier, which can be identified optimally via the variational theory, the subscripts denote the th approximation, and is considered as a restricted variation, that is, .

Also we can find the Lagrange multipliers easily by using integration by parts of (1), but in this paper, the Lagrange multipliers are found to be of the form , and in such a case, the integration is basically the single convolution with respect to , and hence Laplace transform is appropriate to use.

Take Laplace transform of (2); then, the correction functional will be constructed in the form therefore, where is a single convolution with respect to .

To find the optimal value of , we first take the variation with respect to . Thus, then (5) becomes In this paper, we assume that is a linear partial differential operator given by ; then, (6) can be written in the form The extreme condition of requires that . This means that the right hand side of (7) should be set to zero; then, we have the following condition: then, we have the following iteration formula:

#### 3. Applications

In this section, we apply the Laplace variational iteration method for solving some linear and nonlinear partial differential equations in physics.

*Example 1. *Consider the initial linear partial differential equation:
The Laplace variational iteration correction functional will be constructed in the following manner:
or
Take the variation with respect to of (12) to obtain
then we have
The extreme condition of requires that . Hence, we have
Substituting (15) into (11), we obtain
Let ; then, from (16), we have
The inverse Laplace transforms yields
Substituting (18) into (11), we obtain
then, the exact solution of (10) is
We see that the exact solution is coming very fast by using only few terms of the iterative scheme.

*Example 2. *Consider the nonlinear partial differential equation:
The Laplace variational iteration correction functional will be constructed as follows:
or
Take the variation with respect to of (23) and make the correction functional stationary to obtain
This implies that
Substituting (25) into (22), we obtain
or
Let ; then, from (27), we have
then, the exact solution of (21) is
Again the exact solution is coming very fast by using only few terms of the iterative scheme.

*Example 3. *Consider the physics nonlinear boundary value problem
The Laplace variational iteration correction functional is as follows:
or
Take the variation with respect to of the last equation and make the correction functional stationary to obtain
this implies that
Substituting (34) into (31), we obtain
or
Let ; then, from (36), we have
and then, the exact solution of (30) is

#### 4. Conclusion

The method of combining Laplace transforms and variational iteration method is proposed for the solution of linear and nonlinear partial differential equations. This method is applied in a direct way without employing linearization and is successfully implemented by using the initial conditions and convolution integral.

#### Conflict of Interests

The authors declare that there is no conflict of interests regarding the publication of this paper.

#### Acknowledgment

This work was funded by the Deanship of Scientific Research (DSR), King AbdulazizUniversity, Jeddah, under Grant no. (363-008-D1434). The authors, therefore, acknowledge with thanks DSR technical and financial support.

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#### Copyright

Copyright © 2014 Eman M. A. Hilal and Tarig M. Elzaki. 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.