Title: Numerical study of the Kadomtsev--Petviashvili equation and dispersive shock waves,
Abstract: A detailed numerical study of the long time behaviour of dispersive shock
waves in solutions to the Kadomtsev-Petviashvili (KP) I equation is presented.
It is shown that modulated lump solutions emerge from the dispersive shock
waves. For the description of dispersive shock waves, Whitham modulation
equations for KP are obtained. It is shown that the modulation equations near
the soliton line are hyperbolic for the KPII equation while they are elliptic
for the KPI equation leading to a focusing effect and the formation of lumps.
Such a behaviour is similar to the appearance of breathers for the focusing
nonlinear Schrodinger equation in the semiclassical limit.