We present, in the case of a fold Caustic, a closed system for the computation
of the multi-valued solution of the Eikonal equation and the position of the
caustic.
Each phase is solution of an Eikonal equation set in configuration space
(we do not work in phase space) and we derive an ordinary differential
equation for the caustic curve.
This is joint work with O. Lafitte (CEA), R. Sentis (CEA) and I. Solliec
(INRIA).