`Abstract and Applied AnalysisVolume 2012 (2012), Article ID 863583, 10 pageshttp://dx.doi.org/10.1155/2012/863583`
Research Article

## The GDTM-Padé Technique for the Nonlinear Lattice Equations

Hangzhou Institute of Commerce, Zhejiang Gongshang University, Hangzhou 310018, China

Received 22 December 2011; Accepted 28 January 2012

Copyright © 2012 Junfeng Lu. 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.

#### Abstract

The GDTM-Padé technique is a combination of the generalized differential transform method and the Padé approximation. We apply this technique to solve the two nonlinear lattice equations, which results in the high accuracy of the GDTM-Padé solutions. Numerical results are presented to show its efficiency by comparing the GDTM-Padé solutions, the solutions obtained by the generalized differential transform method, and the exact solutions.

#### 1. Introduction

The nonlinear differential difference equations (NDDEs) have wide applications in various branches of science, including the mechanical engineering, condensed matter physics, biophysics, mathematical statistics, control theory and so on [111]. During the past decades, a large number of solution methods such as the Adomian decomposition method [12, 13], the Jacobian elliptic function method [14], the Exp-function method [15], the -expansion method [16], and the variable-coefficient discrete tanh method [17] were proposed to solve the NDDEs. Recently, the generalized differential transform method [1820] combined with the Padé technique (named as GDTM-Padé technique) was presented in [21] to construct the numerical or exact solutions of the differential difference equations. Due to the Padé approximation, the convergence and the accuracy of the original series solutions can be improved.

In this paper, we focus on solving two nonlinear lattice equations by applying the GDTM-Padé technique. The first nonlinear equation is the hybrid lattice equation [5] defined by which was related with the discretization of the KDV equations or the modified KDV equations. The second equation arose in the study of continuum two-boson KP systems [3, 22], which was called as the Volterra lattice equation

The rest of this paper is organized as follows. In Section 2, we introduce the idea of the GDTM-Padé technique for the NDDEs. The hybrid lattice equation and the Volterra lattice equation are studied in Section 3. Numerical results are presented to verify the efficiency. Finally, some conclusions are given.

To illustrate the basic idea of the GDTM-Padé technique, we consider the general nonlinear difference differential equation where is a nonlinear differential operator, is the unknown function with respect to the discrete spatial variable and the temporal variable . Applying the one-dimensional differential transform method (GDTM), the differential transform of the th derivative of the function is defined by The differential inverse transform of is read as Particularly, the function can be formulated as a series when , that is, In the real applications, we can determine the coefficients and obtain the th-order approximation of the function given by The transformed operations for the GDTM are listed in Table 1 [21].

Table 1: The operations for generalized differential transform method.

To improve the accuracy and convergence of the GDTM solution (2.5), the Padé approximation [23, 24] is used. For simplicity, we denote the Padé approximation to by where with the normalization condition . The coefficients of and can be uniquely determined by comparing the first terms of the functions and . In practice, the construction of the Padé approximation involves only algebra equations, which are solved by means of the Mathematica or Maple package. We call the solution obtained by the GDTM and the Padé approximation as the GDTM-Padé solution.

#### 3. Numerical Examples

In this section, we will illustrate the validity and advantages of the GDTM-Padé technique for the nonlinear differential difference equations. Two nonlinear lattice equations will be studied, where one is a hybrid lattice and the other is a Volterra lattice.

##### 3.1. The Hybrid Lattice Equation

Consider the hybrid lattice equation (1.1) with the initial condition The exact solution to (1.1) [2] is of the form

Using the GDTM technique, the transformed problem of (1.1) can be expressed in the following recurrence formula: The transformed initial condition is One can also easily construct the implicit initial conditions as follows:

Based on the above initial conditions and the recursive formula (3.3), we can derive the coefficients one by one and obtain the approximate solution . In this example, we set , and . The 5th-order approximate solution at is given by

Applying the GDTM-Padé technique to the solution (3.6), we get the GDTM Padé approximation:

For comparison, we plot the GDTM solutions , the GDTM-Padé solutions , and the exact solutions of (1.1) in Figure 1. Figure 2 shows the absolute error of the GDTM solutions and the GDTM-Padé solutions. The GDTM solutions are in good agreement with the exact solutions in the small interval , and high errors appear when . By the GDTM-Padé technique, the accuracy of the approximation is improved largely.

Figure 1: The compared results for the GDTM solutions (black), the GDTM-Padé solutions (red), and the exact solutions (blue) of (1.1).
Figure 2: The error curves for the GDTM solutions (blue) and the GDTM-Padé solutions (red).
##### 3.2. The Volterra Lattice Equations

We further consider the two component Volterra lattice equations (1.2) with the initial conditions We remark that the exact solutions to (1.2) [2] are given by and , respectively.

Similarly, using the GDTM-Padé technique, we obtain the following transformed problems: with the initial conditions

We first obtain the coefficients of by the above initial conditions and (3.9), then derive the coefficients of , which results in the GDTM solutions and .

We set , at , and obtain the 6th-order approximations as follows:

The GDTM-Padé solutions to the approximations and can be expressed as

We plot in Figure 3 the curves of the GDTM solutions, the GDTM-Padé solutions, and the exact solutions of (1.2). Figure 4 shows the absolute errors of the GDTM solutions and the GDTM-Padé solutions. The GDTM-Padé method performs better than the GDTM method for this example. We show the absolute errors of and in the left column of Table 2. The absolute errors of and are shown in the right column. Obviously, the errors of are reduced significantly, comparing with the approximation when . This phenomenon also appears in the errors of .

Table 2: Comparisons of the absolute errors between the GDTM solutions and GDTM-Padé solutions for (1.2) with , and .
Figure 3: The compared results for the GDTM solutions (black), the GDTM-Padé solutions (red), and the exact solutions (blue) of (1.2) when , and .
Figure 4: The absolute error curves for the the GDTM solutions (blue) and the GDTM-Padé solutions (red) of (1.2) when , and .

If , at , the 6th-order approximations are given by

Similarly, the GDTM-Padé solutions to (3.14) are

Figure 5 shows the compared results for the solutions including , , and , , . The error curves are plotted in Figure 6. In Table 3, we compare the absolute errors of GDTM solutions and GDTM-Padé solutions. Similar to the previous case, the GDTM-Padé method also outperforms the GDTM method.

Table 3: Numerical results of the absolute errors between the GDTM solutions and the GDTM-Padé solutions for (1.2) with , and .
Figure 5: The compared results for the GDTM solutions (black), the GDTM-Padé solutions (red), and the exact solutions (blue) of (1.2) when , and .
Figure 6: The absolute errors for the the GDTM solutions (blue) and the GDTM-Padé (red) of (1.2) when , and .

#### 4. Conclusions

This paper focused on solving the nonlinear lattice equations by using the GDTM-Padé technique. The numerical results confirmed the effectiveness of this method. In the future work, we will further extend this method to other nonlinear differential difference equations.

#### Acknowledgments

The work of this author was supported by the Natural Science Foundation of Zhejiang Province (Y6110639) and the project Y201016192 of Education Department of Zhejiang Province.

#### References

1. V. E. Adler, S. I. Svinolupov, and R. I. Yamilov, “Multi-component Volterra and Toda type integrable equations,” Physics Letters A, vol. 254, no. 1-2, pp. 24–36, 1999.
2. D. Baldwin, Ü. Göktaş, and W. Hereman, “Symbolic computation of hyperbolic tangent solutions for nonlinear differential-difference equations,” Computer Physics Communications, vol. 162, no. 3, pp. 203–217, 2004.
3. L. Bonora and C. S. Xiong, “An alternative approach to KP hierarchy in matrix models,” Physics Letters B, vol. 285, no. 3, pp. 191–198, 1992.
4. E. Fermi, J. Pasta, and S. Ulam, The Collected Papers of Enrico Fermi, The University of Chicago Press, Chicago, Ill, USA, 1965.
5. R. Hirota and M. Iwao, “Time-discretization of soliton equations,” in SIDE III-Symmetries and Integrability of Difference Equations, vol. 25 of CRM Proceedings & Lecture Notes, pp. 217–229, American Mathematical Society, Providence, RI, USA, 2000.
6. D. Levi and O. Ragnisco, “Extension of the spectral-transform method for solving nonlinear differential difference equations,” Lettere al Nuovo Cimento, vol. 22, no. 17, pp. 691–696, 1978.
7. D. Levi and R. Yamilov, “Conditions for the existence of higher symmetries of evolutionary equations on the lattice,” Journal of Mathematical Physics, vol. 38, no. 12, pp. 6648–6674, 1997.
8. Y. B. Suris, “New integrable systems related to the relativistic Toda lattice,” Journal of Physics A, vol. 30, no. 5, pp. 1745–1761, 1997.
9. Y. B. Suris, “On some integrable systems related to the Toda lattice,” Journal of Physics A, vol. 30, no. 6, pp. 2235–2249, 1997.
10. Y. B. Suris, “Integrable discretizations for lattice system: local equations of motion and their Hamiltonian properties,” Reviews in Mathematical Physics, vol. 11, no. 6, pp. 727–822, 1999.
11. R. I. Yamilov, “Construction scheme for discrete Miura transformations,” Journal of Physics A, vol. 27, no. 20, pp. 6839–6851, 1994.
12. G. Adomian, Solving Frontier Problems of Physics: The Decomposition Method, vol. 60 of Fundamental Theories of Physics, Kluwer Academic Publishers, Dordrecht, The Netherlands, 1994.
13. G. Adomian, “A review of the decomposition method in applied mathematics,” Journal of Mathematical Analysis and Applications, vol. 135, no. 2, pp. 501–544, 1988.
14. C. Dai and J. Zhang, “Jacobian elliptic function method for nonlinear differential-difference equations,” Chaos, Solitons & Fractals, vol. 27, no. 4, pp. 1042–1047, 2006.
15. J.-H. He and X.-H. Wu, “Exp-function method for nonlinear wave equations,” Chaos, Solitons and Fractals, vol. 30, no. 3, pp. 700–708, 2006.
16. M. Wang, X. Li, and J. Zhang, “The ${G}^{\prime }/G$-expansion method and travelling wave solutions of nonlinear evolution equations in mathematical physics,” Physics Letters A, vol. 372, no. 4, pp. 417–423, 2008.
17. S. Zhang and H.-Q. Zhang, “Variable-coefficient discrete tanh method and its application to $\left(2+1\right)$-dimensional Toda equation,” Physics Letters A, vol. 373, no. 33, pp. 2905–2910, 2009.
18. V. S. Erturk, S. Momani, and Z. Odibat, “Application of generalized differential transform method to multi-order fractional differential equations,” Communications in Nonlinear Science and Numerical Simulation, vol. 13, no. 8, pp. 1642–1654, 2008.
19. S. Momani, Z. Odibat, and V. S. Erturk, “Generalized differential transform method for solving a space- and time-fractional diffusion-wave equation,” Physics Letters A, vol. 370, no. 5-6, pp. 379–387, 2007.
20. Z. Odibat, S. Momani, and V. S. Erturk, “Generalized differential transform method: application to differential equations of fractional order,” Applied Mathematics and Computation, vol. 197, no. 2, pp. 467–477, 2008.
21. Z. Li, W. Zhen, and Z. Zhi, “Generalized differential transform method to differential-difference equation,” Physics Letters A, vol. 373, no. 45, pp. 4142–4151, 2009.
22. H. Aratyn, L. A. Ferreira, J. F. Gomes, and A. H. Zimerman, “On two-current realization of KP hierarchy,” Nuclear Physics B, vol. 402, no. 1-2, pp. 85–117, 1993.
23. G. A. Baker, Essential of Padé Approximants, Academic Press, London, UK, 1975.
24. G. A. Baker and P. Graves-Morris, Encyclopedia of Mathematics and its Application 13, Parts I and II: Padé Approximants, Addison-Wesley Publishing Company, New York, NY, USA, 1981.