A stable HLLC Riemann solver for relativistic magnetohydrodynamics

In this short note we improve on an HLLC Riemann solver for relativistic magnetohydrodynamics (MHD). The improvement consists in realizing that density jumps as well as jumps in the transverse velocity can be safely incorporated into the HLLC Riemann solver for relativistic MHD. The iteration process described here is low cost, stable and fast-converging. It obviates the need to have one formulation when the longitudinal magnetic field is non-zero and another when it vanishes. Excellent operation is shown on several test problems.