Alfred Michel GRUNDLAND
Centre de Recherches Mathematiques,
Universite de Montreal,
C.P. 6128,Succ. Centre-ville,
Montreal, (QC)  H3C-3J7 Canada

On conditionally invariant solutions of magnetohydrodynamic equations. Multiple waves

We present a version of conditional symmetry method in order to obtain multiple wave solutions expressed in terms of Riemann invariants. We construct an abelian distribution of vector fields which are symmetries of the original system of PDEs subjected to certain first order differential constraints. The usefulness of our approach is demonstrated on simple and double wave solutions of MHD equations. We also present a comparison of the conditional symmetry method with the generalized method of characteristics.