#### Abstract

This paper presents the boundedness and uniform boundedness of traveling wave solutions for the Kadomtsev-Petviashvili (KP) equation. They are discussed by means of a traveling wave transformation and Lyapunov function.

#### 1. Introduction

We consider the Kadomtsev-Petviashvili (KP) equation: It is well known that Kadomtsev-Petviashvili equation arises in a number of remarkable nonlinear problems both in physics and mathematics. By using various methods and techniques, exact traveling wave solutions, solitary wave solutions, doubly periodic solutions, and some numerical solutions have been obtained in [16].

In this paper, (1) can be changed into an ordinary differential equation by using traveling wave transformation; the boundedness and uniform boundedness of solution for the resulting ordinary differential equation are discussed using the method of Lyapunov function.

#### 2. The Boundedness

Taking a traveling wave transformation in (1), then (1) can be transformed into the following form:

In general, we use the following system, which is equivalent to (2): where

We consider the following system, which is equivalent to (3):

Theorem 1. If the following conditions hold for the system (5):(i) there are positive constants , , , , , and such that (ii),   .(iii).(iv), where is a nonnegative continuous function and .
Then, all the solutions of system (5) are bounded.

Proof. We first construct the Lyapunov function defined by
It follows from conditions (i) and (ii) that Summing up the above discussions, we get
Thus, we deduce that the function defined in (7) is a positive definite function which has infinite inferior limit and infinitesimal upper limit. Hence, there exsits a positive constant such that Taking the total derivative of (7) with respect to along the trajectory of (5), we obtain By using conditions (i) and (iii), it follows that According to (ii), we have Hence,
Thus, all the solutions of system (5) are bounded.

Theorem 2. Let conditions (i)–(iv) of Theorem 1 be satisfied for the system (5), and let the following condition hold: Then, all the solutions of system (5) are uniformly bounded.

Proof. It is clear that the function defined in (7) satisfies the conditions (15), therefore, all the solutions of system (5); are uniformly bounded [7].

#### Acknowledgments

This work was financially supported by the Chinese Natural Science Foundation (11061028) and Yunnan Natural Science Foundation (2010CD086).