  We briefly review the recent numerical works that have been performed to
understand the formation of massive stars. After a brief description of the
classical works, we review more specifically $i)$ the problem of building stars
more massive than 20 $M_\odot$ and $ii)$ how to prevent the massive cores to
fragment in many objects. Multi-D simulations succeed in circumventing the
radiative pressure leading to the formation of massive stars although some
questions are still debated regarding how is accretion exactly proceeding.
While the core fragmentation is slightly reduced by the radiative feedback and
the magnetic field when they are treated separately, it is almost entirely
suppressed when both of them are included. This is because, magnetic field by
removing angular momentum focusses the flow in a compact region. This makes the
radiative feedback very efficient leading to a significant increase of the
temperature.
