Parallel Decomposition of Unstructured FEM-Meshes

We present a massively parallel algorithm for static and dynamic partitioning of unstructured FEM-meshes. The method consists of two parts. First a fast but inaccurate sequential clustering is determined which is used, together with a simple mapping heuristic, to map the mesh initially onto the processors of a massively parallel system. The second part of the method uses a massively parallel algorithm to remap and optimize the mesh decomposition taking several cost functions into account which reeect the characteristics of the underlying hardware and the requirements of the numerical solution method supposed to run after the decomposition. The parallel algorithm rst calculates the amount of nodes that have to be migrated between pairs of clusters in order to obtain an optimal load balancing. In a second step, nodes to be migrated are chosen according to cost functions optimizing the amount of necessary communication and the shapes of subdomains. The latter criterion is extremely important for the convergence behavior of certain numerical solution methods, especially for preconditioned conjugate gradient methods. The parallel parts of the method are implemented in C under Parix to run on the Parsytec GC systems. Results on up to 64 processors are presented and compared to those of other existing methods.