#### Abstract

We use He's polynomials which are calculated form homotopy perturbation method (HPM) for solving heat and wave-like equations. The proposed iterative scheme finds the solution without any discretization, linearization, or restrictive assumptions. Several examples are given to verify the reliability and efficiency of the method. The fact that suggested technique solves nonlinear problems without using Adomian's polynomials is a clear advantage of this algorithm over the decomposition method.

#### 1. Introduction

The heat and wave-like models are the integral part of applied sciences and arise in various physical phenomena. Several techniques including spectral, characteristic, modified variational iteration and Adomian’s decomposition have been used for solving these problems; see [1–3] and the references therein. Most of these techniques encounter a considerable size of difficulty. He [4–11] developed and formulated homotopy perturbation method (HPM) by merging the standard homotopy and perturbation. The homotopy perturbation method (HPM) proved to be compatible with the versatile nature of the physical problems and has been applied to a wide class of functional equations; see [1, 4–19] and the references therein. In this technique, the solution is given in an infinite series usually converging to an accurate solution; see [1, 4–19] and the references therein. It is worth mentioning that HPM is applied without any discretization, restrictive assumption or transformation and is free from round off errors. The HPM is applied for all the nonlinear terms in the problem without discretizing either by finite difference or by spline techniques at the nodes and involves laborious calculations coupled with a strong possibility of the ill-conditioned resultant equations which are a complicated problem to solve. Moreover, unlike the method of separation of variables that requires initial and boundary conditions, the homotopy perturbation method (HPM) provides an analytical solution by using the initial conditions only. The fact that HPM solves nonlinear problems without using Adomian’s polynomials is a clear advantage of this technique over the decomposition method. It is worth mentioning that [12, 13] introduced He’s polynomials by splitting the nonlinear term and proved their compatibility with Adomian’s polynomials coupled with the conclusion that He’s polynomials are easier to calculate, are more user friendly, and are independent of the complexities arising in calculating the so-called Adomian’s polynomials. It is to be highlighted that He’s polynomials are calculated from homotopy perturbation method (HPM). Inspired and motivated by the ongoing research in this area, we use He’s polynomials for solving heat and wave-like equations. It is worth mentioning that Noor and Mohyud-Din [20] introduced a homotopy approach which involves an additional term and consequently leads towards laborious and redundant calculations, whereas the approach used in Section 2 is more precise and easier to implement. Moreover, it reduces the huge unnecessary calculation arising in [20]. Several examples are given to verify the reliability and efficiency of the algorithm.

#### 2. Homotopy Perturbation Method and He’s Polynomials

To explain the homotopy perturbation method, we consider a general equation of the type where is any integral or differential operator. We define a convex homotopy by where is a functional operator with known solutions , which can be obtained easily. It is clear that, for we have This shows that continuously traces an implicitly defined curve from a starting point to a solution function . The embedding parameter monotonically increases from zero to unit as the trivial problem is continuously deforms the original problem . The embedding parameter can be considered as an expanding parameter [1, 2, 4–19]. The homotopy perturbation method uses the homotopy parameter as an expanding parameter [4–11] to obtain if , then (2.5) corresponds to (2.2) and becomes the approximate solution of the form It is well known that series (2.6) is convergent for most of the cases and also the rate of convergence is dependent on ; see [4–11]. We assume that (2.6) has a unique solution. The comparisons of like powers of give solutions of various orders. In sum, according to [12, 13], He’s HPM considers the solution, , of the homotopy equation in a series of as follows: and the method considers the nonlinear term as where ’s are the so-called He’s polynomials [12, 13], which can be calculated by using the formula

#### 3. Numerical Applications

In this section, we use He’s polynomials which are calculated from homotopy perturbation method (HPM) for solving heat and wave-like equations.

*Example 3.1 ([1, 2]). *Consider the one-dimensional initial boundary value problem which describes the heat-like models
with boundary conditions
and initial conditions
Apply the convex homotopy
Compare the coefficient of like powers of
where are He’s polynomials. The series solution is given by
and in a closed form by

*Example 3.2 ([1, 2]). *Consider the two-dimensional initial boundary value problem which describes the heat-like models
with boundary conditions
and initial conditions
Apply the convex homotopy method
Compare the coefficient of like powers of
where are He’s polynomials. The series solution is given by
and in a closed form by

*Example 3.3 ([1, 2]). *Consider the three-dimensional inhomogeneous initial boundary value problem which describes the heat-like models
subject to the boundary conditions
and the initial conditions
Apply the convex homotopy method
Compare the coefficient of like powers of
where are He’s polynomials. The series solution is given by
and in a closed form by

*Example 3.4. *Consider the following nonlinear heat-like model:
subject to the initial conditions
Apply the convex homotopy method
Compare the coefficient of like powers of
where are He’s polynomials. The series solution is given by
and the closed form solution is given as

*Example 3.5 ([1, 2]). *Consider the one-dimensional initial boundary value problem which describes the wave-like models
subject to the boundary conditions
and initial conditions
Apply the convex homotopy method
Compare the coefficient of like powers of
where are He’s polynomials. The series solution is given by
and in a closed form by

*Example 3.6 ([1, 2]). *Consider the two-dimensional initial boundary value problem which describes the wave-like models
subject to the Neumann boundary conditions
and initial conditions
Apply the convex homotopy method
Compare the coefficient of like powers of
where are He’s polynomials. The series solution is given by
and in a closed form by

*Example 3.7 ([1, 2]). *Consider the three-dimensional inhomogeneous initial boundary value problem which describes the wave-like models
subject to the boundary conditions
and the initial conditions
Apply the convex homotopy method
Compare the coefficient of like powers of and proceede as before, the series solution is given by
and in a closed form by

#### 4. Conclusion

In this paper, we use He’s polynomials which are calculated from homotopy perturbation method (HPM) for solving heat and wave-like equations. The method is applied in a direct way without using linearization, transformation, discretization, or restrictive assumptions. It may be concluded that the proposed scheme is very powerful and efficient in finding the analytical solutions for a wide class of boundary value problems. The method gives more realistic series solutions that converge very rapidly in physical problems. It is also observed that He’s polynomials are compatible with Adomian’s Polynomials but are easier to calculate and are more user friendly.

#### Acknowledgments

The author is highly grateful to the referees and Professor Dr. Ji-Huan He for their very constructive comments. The author would like to thank Brig (R) Qamar Zaman, Vice Chancellor, HITEC University, Taxila Cantt, Pakistan for the provision of conducive environs for research.