HYDRA - A PARALLEL ADAPTIVE-GRID CODE

We describe the first parallel implementation of an adaptive particle- particle, particle-mesh code with smoothed particle hydrodynamics. Par allelisation of the serial code, ''Hydra'', is achieved by using CRAFT , a Cray proprietary language which allows rapid implementation of a s erial code on a parallel machine by allowing global addressing of dist ributed memory. The collisionless variant of the code has already comp leted several 16.8 million particle cosmological simulations on a 128 processor Cray T3D whilst the full hydrodynamic code has completed sev eral 4.2 million particle combined gas and dark matter runs. The effic iency of the code now allows parameter-space explorations to be perfor med routinely using 64(3) particles of each species. A complete run in cluding gas cooling, from high redshift to the present epoch requires approximately 10 hours on 64 processors. In this paper we present impl ementation details and results of the performance and scalability of t he CRAFT version of Hydra under varying degrees of particle clustering . (C) 1997 Elsevier Science B.V.