“…The study of soliton stability in nonlinear optical materials has a long history, also associated with the study of nonlinear waves in other media such as plasmas and fluids. Stability of one-parameter solitary waves has already been well understood for both fundamental (singlehump and nodeless) solitons [2,3,4,5] and solitons with nodes and multiple humps [6,7]. The pioneering results of N. Vakhitov and A. Kolokolov [2], known these days as the Vakhitov-Kolokolov stability criterion, found their rigorous justification in a general mathematical theory developed by M. Grillakis et al [8].…”