  Obtaining a stable magnetohydrodynamical (MHD) formalism in SPH - i.e.
smoothed particle magnetohydrodynamics (SPMHD) - has proven remarkably
difficult. To implement MHD requires two steps: a modification to the momentum
equation and an induction equation, and both present challenges. We first
provide an overview of how SPMHD is implemented, and then discuss how this
implementation fails and the limitation of various corrective methods - with
particular reference to the effects of particle disorder. Although there are
many problems for which, with careful choice of corrective measures, good
results can be obtained, we then show that, at the very limits of the state of
the art, the ability to perform stable MHD calculations in SPH is curtailed by
numerical issues.
