HYDRA-MPI: An Adaptive Particle-Particle, Particle-Mesh code for conducting Cosmological Simulations on MPP Architectures

We discuss the design and implementation of a parallel adaptive PM code, for massively parallel architectures. The code, although primarily designed for conducting gravitational simulations in a cosmological context, also includes a Smoothed Particle Hydrodynamics solver. The code is written in a combination of C, FORTRAN 77 and FORTRAN 90. The MPI-2 remote memory access standard is used for one-sided message passing thereby enabling more time to be spent in raw computation. The design decision has lead to a number of interesting problems and circumstances, which we discuss in detail. Raw performance figures are presented in terms of numbers of particles per second to compare to alternative codes.