  An adaptation of the Particle-Particle/Particle-Mesh (P3M) code to the
special purpose hardware GRAPE is presented. The short range force is
calculated by a four chip GRAPE-3A board, while the rest of the calculation is
performed on a Sun Sparc 10/51 workstation. The limited precision of the GRAPE
hardware and algorithm constraints introduce stochastic errors of the order of
a few percent in the gravitational forces. Tests of this new P3MG3A code show
that it is a robust tool for cosmological simulations. The code currently
achieves a peak efficiency of one third the speed of the vectorized P3M code on
a Cray C-90 and significant improvements are planned in the near future.
Special purpose computers like GRAPE are therefore an attractive alternative to
supercomputers for numerical cosmology.
