A class of periodic solutions of nonlinear envelope equations, e.g., t
he nonlinear Schrodinger equation (NLS), is expressed in terms of rati
onal functions of elliptic functions. The Hirota bilinear transformati
on and theta functions are used to extend and generalize this class of
solutions first reported for NLS earlier in the literature. In partic
ular a higher order NLS and the Davey-Stewartson (DS) equations are tr
eated. Doubly periodic standing waves solutions are obtained for both
the DSI and DSII equations. A symbolic manipulation software is used t
o confirm the validity of the solutions independently. (C) 1995 Americ
an Institute of Physics.