Comparison of selected FETI coarse space projector implementation strategies

Abstract

This paper deals with scalability improvements of the FETI (Finite Element Tearing and Interconnecting) domain decomposition method solving elliptic PDEs. The main bottleneck of FETI is the solution of a coarse problem that is part of the projector onto the natural coarse space. This paper introduces and compares two strategies for the FETI coarse problem solution. The first one is a classical solution with either direct (factorization + forward/backward substitutions) or iterative solvers (conjugate gradient and deflated conjugate gradient methods). The second one is the assembly of an explicit inverse using a direct solver with the coarse problem solution realised by dense matrix-vector products. MPI subcommunicators are employed to increase arithmetic intensity and, crucially, to decrease the communication cost. PERMON library for quadratic programming implementing the Total FETI variant of FETI was used for the numerical experiments.