  An implicit method for radiative transfer in SPH is described. The diffusion
approximation is used, and the hydrodynamic calculations are performed by a
fully three--dimensional SPH code. Instead of the energy equation of state for
an ideal gas, various energy states and the dissociation of hydrogen molecules
are considered in the energy calculation for a more realistic temperature and
pressure determination. In order to test the implicit code, we have performed
non--isothermal collapse simulations of a centrally condensed cloud, and have
compared our results with those of finite difference calculations performed by
MB93. The results produced by the two completely different numerical methods
agree well with each other.
