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A Multilevel Schwarz Preconditioner Based on a Hierarchy of Robust Coarse Spaces

Hussam Al Daas 1 Laura Grigori 1 Pierre Jolivet 2, 3 Pierre-Henri Tournier 4
1 ALPINES - Algorithms and parallel tools for integrated numerical simulations
INSMI - Institut National des Sciences Mathématiques et de leurs Interactions, Inria de Paris, LJLL (UMR_7598) - Laboratoire Jacques-Louis Lions
2 IRIT-APO - Algorithmes Parallèles et Optimisation
IRIT - Institut de recherche en informatique de Toulouse
Abstract : In this paper we present a multilevel preconditioner based on overlapping Schwarz methods for symmetric positive definite (SPD) matrices. Robust two-level Schwarz preconditioners exist in the literature to guarantee fast convergence of Krylov methods. As long as the dimension of the coarse space is reasonable, that is, exact solvers can be used efficiently, two-level methods scale well on parallel architectures. However, the factorization of the coarse space matrix may become costly at scale. An alternative is then to use an iterative method on the second level, combined with an algebraic preconditioner, such as a one-level additive Schwarz preconditioner. Nevertheless, the condition number of the resulting preconditioned coarse space matrix may still be large. One of the difficulties of using more advanced methods, like algebraic multigrid or even two-level overlapping Schwarz methods, to solve the coarse problem is that the matrix does not arise from a partial differential equation (PDE) anymore. We introduce in this paper a robust multilevel additive Schwarz preconditioner where at each level the condition number is bounded, ensuring a fast convergence for each nested solver. Furthermore, our construction does not require any additional information than for building a two-level method, and may thus be seen as an algebraic extension.
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Submitted on : Monday, December 7, 2020 - 10:24:44 AM
Last modification on : Tuesday, October 19, 2021 - 2:24:23 PM

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Hussam Al Daas, Laura Grigori, Pierre Jolivet, Pierre-Henri Tournier. A Multilevel Schwarz Preconditioner Based on a Hierarchy of Robust Coarse Spaces. SIAM Journal on Scientific Computing, Society for Industrial and Applied Mathematics, 2021, 43 (3), pp.A1907-A1928. ⟨10.1137/19M1266964⟩. ⟨hal-02151184v2⟩

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