  In this paper we study the general relationship between the evolutionary
conditions for discontinuous solutions of hyperbolic conservation laws with a
concave entropy function and the existence and uniqueness of steady dissipative
shock structure. Our results confirm the classical shock theory. We also show
that the appearance of intermediate shocks in numerical MHD simulations can be
understood in terms of the equations planar magnetohydrodynamics for which some
of these shocks turn out to be evolutionary. Finally, we discuss ways in which
numerical schemes can be modified in order to avoid the appearance of
intermediate shocks in simulations with such symmetry.
