  Radiative transfer plays a key role in the star formation process. Due to a
high computational cost, radiation-hydrodynamics simulations performed up to
now have mainly been carried out in the grey approximation. In recent years,
multi-frequency radiation-hydrodynamics models have started to emerge, in an
attempt to better account for the large variations of opacities as a function
of frequency. We wish to develop an efficient multigroup algorithm for the
adaptive mesh refinement code RAMSES which is suited to heavy proto-stellar
collapse calculations. Due to prohibitive timestep constraints of an explicit
radiative transfer method, we constructed a time-implicit solver based on a
stabilised bi-conjugate gradient algorithm, and implemented it in RAMSES under
the flux-limited diffusion approximation. We present a series of tests which
demonstrate the high performance of our scheme in dealing with
frequency-dependent radiation-hydrodynamic flows. We also present a preliminary
simulation of a three-dimensional proto-stellar collapse using 20 frequency
groups. Differences between grey and multigroup results are briefly discussed,
and the large amount of information this new method brings us is also
illustrated. We have implemented a multigroup flux-limited diffusion algorithm
in the RAMSES code. The method performed well against standard
radiation-hydrodynamics tests, and was also shown to be ripe for exploitation
in the computational star formation context.
