National Partnership for Advanced Computational Infrastructure

1. -6.47x10-9 0 1.31x10-9 National Partnership for Advanced Computational Infrastructure University of California, San Diego The Scallop Solver LibraryGreg Balls and Scott B. Baden Scallopis a library of solvers for elliptic partial differential equations on regular block-structured domains. Scallop is designed to be scalable latency tolerant. Latency is hidden algorithmically by taking advantage of the locality properties of the solution. Most iterative methods communicate frequently to update boundary conditions. Scallop communicates data among processors only twice: first to build a coarse approximation of the right hand side, and second to correct the local boundary conditions with fine grid data. The Scallop library is built on top of the KeLP programming system and runs on a variety of machines, including NPACI’s Blue Horizon. Scallop takes advantage of locality of the solution. Since the solution of an elliptic PDE is a smooth function in the far field, far field data can be accurately represented by a much coarser mesh. This allows us to eliminate the need for iterative communication updates. Only two communication steps are required to calculate fully resolved solutions. The first communication step constructs a global right hand side using information from initial local solutions. After the coarse grid solution has been found, processors communicate a second time to calculate local fine grid boundary conditions. Scallop implements its non-iterative domain decomposition algorithm like this: for each local grid { calculate_local_approximation } communicate_coarse_grid calculate_coarse_solution communicate_fine_boundary_data for each local grid { calculate_final_solution } Collaboration:Scallop is built on the KeLP programming system. Scallop is being developed in collaboration with the PTE/MolSci Alpha project, “Adaptive Computations Applied to Simulation of Fluids in Biological Systems”, and may be used as a solver within that project. Domain decomposition does not strongly affect the solution error Communication time does not overwhelm the total solution time Computation time per point is good when the amount of work per node is reasonably large Scallop codeand further informationis available for download from http://www-cse.ucsd.edu/groups/hpcl/scg/scallop.html