Rational formal solutions of differential-difference equations

In this paper, we study rational formal solutions of differential-difference equations by using a generalized ansätz. With the help of symbolic computation Maple, we obtain many explicit exact solutions of differential-difference equations(DDEs). The solutions contain solitary wave solutions and periodic wave solutions. The (2 + 1)-dimensional Toda lattice equation, relativistic Toda lattice equation and the discrete mKdV equation are chosen to illustrate our algorithm.     

A systematic method for solving differential-difference equations

A systematic method for searching travelling-wave solutions to differential-difference equations (DDEs) is proposed in the paper. First of all, we introduce Bäcklund transformations for the standard Riccati equation which generate new exact solutions by using its simple and known solutions. Then we introduce a kind of formal polynomial solutions to DDEs and further determine the explicit forms by applying the balance principle. Finally, we work out exact solutions of the DDEs via substituting the form solutions and solving over-determined algebraic equations with the help of Maple. As illustrative examples, we obtain the travelling-wave solutions of the (2 + 1)-dimensional Toda lattice equation, the discrete modified KdV (mKdV) equation, respectively.     

Two-periodic waves and asymptotic property for generalized 2D Toda lattice equation

In this paper, two-periodic wave solutions are constructed for the (2 + 1)-dimensional generalized Toda lattice equation by using Hirota bilinear method and Riemann theta function. At the same time, we analyze in details asymptotic properties of the two-periodic wave solutions and give their asymptotic relations between the periodic wave solutions and the soliton solutions.     

The applications of the gauge transformation for the BKP hierarchy

In this paper, we investigated four applications of the gauge transformation for the BKP hierarchy. Firstly, it is found that the orbit of the gauge transformation for the constrained BKP hierarchy defines a special (2+1)$(2+1)$-dimensional Toda lattice equation structure. Then the tau function of the BKP hierarchy generated by the gauge transformation is shown to be the Pfaffian. And the higher Fay-like identities for the BKP hierarchy is also obtained through the gauge transformation. At last, the compatibility between the additional symmetry and the gauge transformation of the BKP hierarchy is proven.     

Soliton-like and periodic form solutions to (2 + 1)-dimensional Toda equation

In this paper, we present a further extended tanh method for constructing exact solutions to nonlinear difference-differential equation(s) (NDDEs) and Lattice equations. By using this method via symbolic computation system MAPLE, we obtain abundant soliton-like and period-form solutions to the (2 + 1)-dimensional Toda equation. Solitary wave solutions are merely a special case in one family. This method can also be used to other nonlinear difference differential equations.     

(2+1)维拟线性扩散方程的不变集和精确解

研究(2+1)维拟线性扩散方程的精确解问题.运用推广的不变集方法,给出(2+1)维拟线性扩散方程的一些特殊解.此方法是(1+1)维拟线性扩散方程的推广.     

Decomposition of a 2 + 1-dimensional Volterra type lattice and its quasi-periodic solutions

A 2 + 1-dimensional Volttera type lattice is proposed. Resorting to the nonlinearization of Lax pair, the 2 + 1-dimensional Volttera type lattice is decomposed into the known 1+1-dimensional differential-difference equations. The relation between a new 2 + 1-dimensional differential-difference equation, certain 1+1-dimensional continuous evolution equations and the known 1+1-dimensional differential-difference equations is discussed. Based on finite-order expansion of the Lax matrix, we introduce elliptic coordinates, from which the two 2 + 1-dimensional differential-difference equations are separated into solvable ordinary differential equations. The evolution of various flows is explicitly given through the Abel–Jacobi coordinates. Quasi-periodic solutions for the two 2 + 1-dimensional differential-difference equations are obtained.     

q-Discretization of the two-dimensional Toda equations

q-Discrete versions of the two-dimensional Toda molecule equation and the two-dimensional Toda lattice equation are proposed through the direct method. The Bäcklund transformation and the Lax pair of the former are obtained. Moreover, the reduction to theq-discrete cylindrical Toda equations is also discussed.Department of Electronical Engeneering, Doshisha University, Kyoto 610-03, Japan. Research Institute for Mathematical Sciences, Kyoto University, Kyoto 606, Japan. (On leave from Department of Applied Mathematics, Faculty of Engineering, Hiroshima University.) Department of Mathematical Sciences, University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153, Japan. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 99, No. 3, pp. 390–398, June, 1994.     

2D Toda lattice equation with self-consistent sources: Casoratian type solutions,bilinear Bäcklund transformation and Lax pair

The two-dimensional Toda lattice equation with self-consistent sources is proposed based on its bilinear forms. Casoratian-type solutions and Bäcklund transformation (BT) for the bilinear forms are presented. Starting from the BT, a Lax pair is derived for the 2D Toda lattice with self-consistent sources.     

Constructing exact solutions to discrete systems with the trial function method

Based on the homogenous balance method and the trial function method, several trial function methods composed of exponential functions are proposed and applied to nonlinear discrete systems. With the.help of symbolic computation system, the new exact solitary wave solutions to discrete nonlinear mKdV lattice equation, discrete nonlinear （2 ＋ 1） dimensional Toda lattice equation, Ablowitz-Ladik-lattice system are constructed.The method is of significance to seek exact solitary wave solutions to other nonlinear discrete systems.     

Multiple lump solutions of the (3+1)-dimensional potential Yu–Toda–Sasa–Fukuyama equation

The bilinear method is employed to construct the multiple lump solutions of the (3+1)-dimensional potential Yu–Toda–Sasa–Fukuyama equation in fluid dynamics. The 1-lump solutions, 3-lump solutions and 6-lump solutions are explicitly presented. The centers of the 3-lump wave have a triangular structure, and the 6-lump wave possesses a central peak and five peaks in a ring. The dynamic characteristics of the obtained solutions are analyzed with the aid of numerical simulation.     

The Darboux transformation associated with two-parameter lattice soliton equation

A new discrete matrix spectral problem with two arbitrary constants is introduced. The corresponding two-parameter integrable lattice soliton equation is obtained through the discrete zero curvature representation, and the resulting integrable lattice equation reduce to the Toda lattice in rational form for a special choice of the parameters. A Darboux transformation (DT) for the lattice soliton equation is constructed. As an application, an explicit solution of the two-parameter lattice soliton equation is presented.     

The ( \frac{G'}{G}) -expansion method and its applications to some nonlinear evolution equations in the mathematical physics

In the present paper, we construct the traveling wave solutions involving parameters for some nonlinear evolution equations in the mathematical physics via the (2+1)-dimensional Painlevé integrable Burgers equations, the (2+1)-dimensional Nizhnik-Novikov-Vesselov equations, the (2+1)-dimensional Boiti-Leon-Pempinelli equations and the (2+1)-dimensional dispersive long wave equations by using a new approach, namely the ( $\frac{G'}{G})$ -expansion method, where G=G(ξ) satisfies a second order linear ordinary differential equation. When the parameters are taken special values, the solitary waves are derived from the traveling waves. The traveling wave solutions are expressed by hyperbolic, trigonometric and rational functions.     

（3＋1）维带有源项的反应扩散方程的不变集和精确解

讨论了（3＋1）维带有源项的反应扩散方程ut=A1（u）uxx＋A2（u）uyy＋A3（u）uzz＋B1（u）ux^2;＋B2（u）uy^2＋B3（u）uz^2＋Q（u）．通过构建函数不变集的思想方法．得到了上述方程的几个新精确解．该方法也可以用来解N＋1维反应扩散方程．     

Bäcklund-Schlesinger transformations for Davey-Stewartson equations

It is shown that integrable (1+2)-dimensional Davey-Stewartson (DS) and Boiti-Leon-Pempinelli (BLP) equations admit an explicit invertible Bäcklund auto-transformation. An algorithm is developed to construct exact solutions for flat- and horseshoe-type solitons of the DS system. Successive application of these transformations allows us to find solutions of (1+1)- and (0+2)-dimensional Toda lattice equations. We point out a similar auto-transformation for analogues of the DS system realized for an arbitrary associative algebra with a unity, in particular, for matrix DS equations. We also relate the (1+2)-dimensional models that we construct to (1+1)-dimensional J-S-systems.Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 109, No. 3, pp. 338–346, December, 1996.     

Similarity solutions of dispersive long-wave equations in two space dimensions

In this paper, both the direct method and the non-classical Lie approach are applied to reduce the (2 + 1)-dimensional dispersive long wave equations. Nine types of two-dimensional PDE reductions and 13 types of ODE reductions are given. All the known reductions obtained by the classical Lie approach are reobtained as some special cases. Similar to the (1 + 1)-dimensional case, some types of reductions with essential and logarithmic singular characteristic manifolds are allowed although the model is integrable.     

New exact solutions to the CDF equations

New exact soliton solutions to the Cologero–Degasperies–Fokas (CDF) equations in (1+1)-dimension and (2+1)-dimension by using the improved tanh method are investigated. First, the (1+1)-dimensional CDF equation is analyzed. By the improved tanh method, the corresponding nonlinear partial differential equation is reduced to the nonlinear ordinary differential equations and then the different types of exact solutions to the original equation are obtained based on the solutions of the Riccati equation. For the case of (2+1)-dimensional CDF equation the same computation procedure is carried out. It is presented that one could obtain new exact explicit solutions, which are traveling wave solutions, to (2+1)-dimensional CDF equation. Additionally, some graphical representations of the solitary and periodic solutions are presented.     

A note on exact complex travelling wave solutions for (2+1)-dimensional B-type Kadomtsev-Petviashvili equation

The -expansion method can be used for constructing exact travelling wave solutions of real nonlinear evolution equations. In this paper, we improve the -expansion method and explore new application of this method to (2+1)-dimensional B-type Kadomtsev-Petviashvili (BKP) equation. New types of exact complex travelling wave solutions of (2+1)-dimensional BKP equation are found. Some exact solutions of (2+1)-dimensional BKP equation obtained before are special cases of our results in this paper.     

Kink solutions for three new fifth order nonlinear equations

In this work we examine three new fifth order nonlinear evolution equations. The simplified form of the Hirota’s direct method is used to derive multiple kink solutions for the first two (1+1)-dimensional equations, and only two soliton solutions for the third (2+1)-dimensional equation. The dispersion relation is the same for the first two equations whereas the third one possesses a different dispersion relation.     

A RIEMANN-HILBERT PROBLEM IN A RIEMANN SURFACE

One of the inspirations behind Peter Lax’s interest in dispersive integrable systems, as the small dispersion parameter goes to zero, comes from systems of ODEs discretizing 1-dimensional compressible gas dynamics [17]. For example, an understanding of the asymptotic behavior of the Toda lattice in different regimes has been able to shed light on some of von Neumann’s conjectures concerning the validity of the approximation of PDEs by dispersive systems of ODEs. Back in the 1990s several authors have worked on the long time asymptotics of the Toda lattice [2, 7, 8, 19]. Initially the method used was the method of Lax and Levermore [16], reducing the asymptotic problem to the solution of a minimization problem with constraints (an "equilibrium measure" problem). Later, it was found that the asymptotic method of Deift and Zhou (analysis of the associated Riemann-Hilbert factorization problem in the complex plane) could apply to previously intractable problems and also produce more detailed information. Recently, together with Gerald Teschl, we have revisited the Toda lattice; instead of solutions in a constant or steplike constant background that were considered in the 1990s we have been able to study solutions in a periodic background. Two features are worth noting here. First, the associated Riemann-Hilbert factorization problem naturally lies in a hyperelliptic Riemann surface. We thus generalize the Deift-Zhou "nonlinear stationary phase method" to surfaces of nonzero genus. Second, we illustrate the important fact that very often even when applying the powerful Riemann-Hilbert method, a Lax-Levermore problem is still underlying and understanding it is crucial in the analysis and the proofs of the Deift-Zhou method!