A New Integrable Variable-Coefficient 2 + 1-Dimensional Long Wave-Short Wave Equation and the Generalized Dressing Method Su,

Based on the generalized dressing method, we propose a new integrable variable-coefficient 2+1-dimensional long wave-short wave equation and derive its Lax pair. Using separation of variables, we have derived the explicit solutions of the equation. With the aid of Matlab, the curves of the solutions are drawn.


Introduction
It is well known that the interactions of long wave and short wave play an important role in fluid dynamics. The model is described by the following equation: The inverse scattering technique proposed in [1] plays an important role in constructing the complete solution of the long wave and short wave resonance equations. The soliton solution of long wave and short wave has been obtained in [2]. Radha et al. in [3] derived periodic solutions and localized solutions of (1). Lai and Chow in [4] studied positon and dromion solutions of 2 + 1-dimensional long wave and short wave resonance interaction equations. Researchers have focused on the long wave and short wave equation [5][6][7][8][9][10] by using different methods. Serkin et al. [11] discussed integrable variable-coefficient nonlinear evolution equations. By utilizing the exp-function method, the generalized solitary solution and periodic solution of soliton equations can be given in [12]. Authors in [13] discussed the interactions of dark soliton and bright soliton in a double-mode optical fiber. In [14,15], authors (Dai and Jeffrey [14], Jeffrey and Dai [15]) extended the dressing method [16,17] to a generalized version for solving soliton equations associated with matrix nonspectral problems and variable-coefficient cases. The generalized dressing method was based on the problems of factorization of an integral operator on the line into the product of two Volterra type integral operators ± , from which the Gel'fand-Levitan-Marchenko (GLM) equation is obtained. These Volterra operators are then used to construct dressed operators ( 1 , 2 ) starting from a pair of initial operators ( 1 , 2 ). Integrable variable-coefficient nonlinear equations are obtained from the compatibility of the dressed operators. There are some differences between the original dressing method and the generalized dressing method. In the original dressing method, the constant coefficient operators have transformed into different constant coefficient operators. The generalized dressing method transforms the variablecoefficient operators into different variable-coefficient ones. The advantages in the generalized dressing method lie in deriving integrable variable-coefficient nonlinear evolution equation and corresponding Lax pairs. However, the original dressing method is a system way to study constant coefficient nonlinear evolution equation [18][19][20]. Authors (Dai and Jeffrey [14]) presented the generalized dressing method; we also discussed some integrable variable-coefficient evolution equations [21][22][23][24][25]. In fact, the dressing method can 2 Advances in Mathematical Physics be thought as a rather general formulation of the inverse scattering method, which has the advantage of bypassing the scattering problem. The common point between the two methods is that two methods can deal with the initial boundary value problem.
In the paper, we applied the generalized dressing method to derive a new integrable variable-coefficient 2 + 1dimensional long wave-short wave equation: where 2 and 2 are functions of and . 1 and 1 are functions of . Particularly, the above equation is reduced to a new 2 + 1-dimensional integrable variable-coefficient equation: in view of 2 = 2 . Furthermore, under the transformations 1 = 1, 1 = 1/ , (3) can be read as the cylindrical equation: Moreover, (2) are written as a 2 + 1-dimensional integrable modified long wave-short wave equation for 2 = 2 and 1 = 1 : The outline of the paper is as follows. In Section 2, we briefly describe the generalized dressing method and its properties. Moreover, we introduce two dressing operators. In Section 3, new integrable variable-coefficient 2 + 1-dimensional long wave-short wave equations and their Lax pairs are derived with the aid of the generalized dressing method. In Section 4, as an application, we obtain explicit solutions of these equations and draw the curves of the solutions.

The Generalized Dressing Method and Dressing Operators
First, we consider three integral operators F( , , ), K + ( , , ), and K − ( , , ) defined by [16] We assume that (I + K + ) −1 exists and F admits the triangular factorization where I is the identity operator. From (7), a direct calculation shows that F and K + satisfy the Gel'fand-Levitan-Marchenko (GLM) equation [16]: here it is supposed that ± ( , , ) and ( , , ) satisfy the condition We now introduce two differential operators M 1 and M 2 defined by with 1 and 1 being matrix functions of . 2 and 2 are matrix functions of and : Suppose that the operator F commutes with M 1 and M 2 ; that is, which together with (10) implies the following equations: Advances In what follows, we obtain the dressing operators N 1 and N 2 with the aid of operators M 1 and M 2 . The dressing procedure is accomplished through the relations [14,15] N 1 (I + K + ) − (I + K + ) M 1 = 0, (15a) The difference between the original dressing method and the generalized dressing method lies in the differential operators M 1 and M 2 which satisfied the relation with 1 and 2 being arbitrary functions of their arguments.

A New Integrable Variable-Coefficient 2+1-Dimensional Long Wave-Short Wave Equation and Its Lax Pair
In this section, based on the generalized dressing method, we derive a new integrable variable-coefficient 2+1-dimensional long wave-short wave equation. From (17), we have We denotê In view of (16), we have 2̂12 + 2̂12̂22 + 2 12 = = 0, Based on (18) and (22)- (23), we obtain (2) (1) 0 From (20), we derive new integrable variable-coefficient 2+1dimensional long wave-short wave equation with the aid of (22)-(26): Particularly, the above equations are reduced to the cylindrical form: Particularly, we consider the case for = ; then (28) is reduced to a new coupled equation:

Explicit Solutions and the Curves of Solutions
In this section, we shall apply the generalized dressing method to construct explicit solutions of these obtained 2 + 1-dimensional long wave-short wave equation and its reductions. We assume that and have solutions in the form of separation of variables: and is the Kronecker delta. We denote = ( ) 2×2 , and, in view of (13) and (14), we obtain 1 11 + 1 ( 11 + 11 ) = 0, 2 11 − 2 ( 11 + 11 ) = 0, In the what follows, we obtain one soliton solution for the case of = 1 of (30). Let ( , , , ) = ( , , ) ( , , ) = ( Then, from (32) we obtain with Δ = 1 − 1  Using (22), we obtain the solutions of (27). Particularly, for 2 = 2 , 1 = 1, and 1 = 1/ , we derive the solutions of (28). In what follows, we draw the curves of the solutions for 2 = 2 , 1 = 1, and 1 = . Figures 1 and 2 describe the imaginary of and real of , respectively. From the curves, we can see that the forms are similar. The imaginary of V and real of V are shown by Figures 3 and 4, respectively. From the curves, we can see that the forms are different and with diminishing energy. Figures 5 and 6 construct the imaginary of and real of , respectively. In view of the solution curves, we can read the difference between the imaginary of and real of . Furthermore, we find that imaginary of V and that of are similar. At the same time, we find that real of V and that of are similar. Similarly, in later paper, we will discuss two soliton solutions and −soliton solutions.

Data Availability
No data were used to support this study.

Conflicts of Interest
The authors declare that there are no conflicts of interest regarding the publication of this paper.