1 Introduction It is not uncommon to encounter the assertion that the dynamical evolution of the large-scale bulk velocity v of a collisionless gas is not described by the hydrodynamic (HD) equations. A favorite " reason " is the statement that pressure cannot be defined in the absence of collisions. Then in some quarters it is believed that the large-scale bulk dynamics of a swirling magnetize...

Iharm3D is an open-source C code for simulating black hole accretion systems in arbitrary stationary spacetimes using ideal general-relativistic magnetohydrodynamics (GRMHD). It implementation of the HARM ("High Accuracy Relativistic Magnetohydrodynamics") algorithm outlined Gammie et al. (2003) with updates as McKinney & (2004) and Noble (2006). The most directly derived from Ryan (2015) but r...