New doubly periodic solutions of (2+1)-dimensional nonlinear wave equations via the generalized sine-Gordon equation expansion method

A generalized sine-Gordon equation expansion method is developed using the famous sine-Gordon equation and a generalized transformation. The method is simple and more powerful than the known sine-cosine method and its extensions, as well as the sn- and cn-function method, for seeking more types of exact solutions of nonlinear wave equations. With the aid of Maple, we choose the (2+1)-dimensional modified KP equation and (2+1)-dimensional coupled Davey-Stewartson equation to illustrate this method. As a consequence many types of new doubly-periodic solutions are obtained. When the modulus m 1 the corresponding solutions reduce to solitary waves and their extensions. This method can be applied to the nonlinear wave equations in mathematical physics and carried out on a computer by the aid of Maple.