“…Whitham theory does not require integrability of the original PDE, and therefore it can also be applied to non-integrable PDEs. Thanks to Whitham theory and, when applicable, the inverse scattering transform (IST), much is known about small dispersion limits for (1+1)-dimensional nonlinear wave equations (e.g., see [13,21,25,30,38,45] and references therein). On the other hand, small dispersion limits for (2+1)dimensional systems have been much less studied and (3+1)-dimensional systems apparently have not been studied at all.…”