Numerical Relativity in a Distributed Environment

The Cactus parallel simulation framework provides a modular and extensible set of components for solving relativity problems on parallel computers. In recent work, we have investigated techniques that would enable the execution of Cactus applications in wide area \computational grid" environments. In a rst study, we investigated the feasibility of distributing a single simulation across multiple supercomputers, while in a second we studied techniques for reducing communication costs associated with remote visualization and steering. Distributed simulation was achieved by using MPICH-G, an implementation of the Message Passing Interface standard that uses mechanisms provided by the Globus grid toolkit to enable wide area execution. Experiments were performed across SGI Origins and Cray T3Es with geographical separations ranging from hundreds to thousands of kilometers. Total execution time when distributed increased by between 48% and 133%, depending on con guration. We view these results as encouraging as they were obtained with essentially no specialized algorithmic structures in the Cactus application. Work on remote visualization focused on the development of a Cactus module that computes isosurfaces inline with numerical relativity calculations. Experiments demonstrated that this technique can reduce network bandwidth requirements by a factor ranging from 2.5 to 114, depending on the nature of the problem.