ON THE STABILITY OF SOLITARY-WAVE SOLUTIONS OF MODEL-EQUATIONS FOR LONG WAVES

After a review of the existing state of affairs, an improvement is mad e in the stability theory for solitary-wave solutions of evolution equ ations of Korteweg-de Vries-type modelling the propagation of small-am plitude long waves. It is shown that the bulk of the solution emerging from initial data that is a small perturbation of an exact solitary w ave travels at a speed close to that of the unperturbed solitary wave. This not unexpected result lends credibility to the presumption that the solution emanating from a perturbed solitary wave consists mainly of a nearby solitary wave. The result makes use of the existing stabil ity theory together with certain small refinements, coupled with a new expression for the speed of propagation of the disturbance. The idea behind our result is also shown to be effective in the context of one- dimensional regularized long-wave equations and multidimensional nonli near Schrodinger equations.