WHITHAM EQUATIONS IN THE AKNS SCHEME

A general method is formulated for the derivation of the modulation Wh itham equations of periodic solutions to integrable equations describe d by the AKNS scheme. The method provides the Whitham equations in a f orm convenient for applications. It is illustrated by the derivation o f a new form of the Whitham equations corresponding to the modulation of one- and two-phase periodic solutions of the nonlinear Schrodinger equation.