On Billiard Solutions of Nonlinear PDE's
Alber, M. S., R. Camassa, Y. N. Fedorov, D. D. Holm, and J. E. Marsden
Physics Letters A 264, 171-178
Abstract:
This letter presents some special features of a class of integrable PDE's
admitting billiard-type solutions, which set them apart from equations whose
solutions are smooth, such as the KdV equation. These billiard solutions are
weak solutions that are piecewise smooth and have first derivative discontinuities
at peaks in their profiles. A connection is established between the peak
locations and nite dimensional billiard systems moving inside n-dimensional
quadrics under the eld of Hooke potentials. Points of reflection are described
in terms of theta-functions and are shown to correspond to the location of
peak discontinuities in the PDE's weak solutions. The dynamics of the peaks
is described in the context of the algebraic-geometric approach to integrable
systems.