# A multilevel algebraic error estimator and the corresponding iterative solver with $p$-robust behavior

* Corresponding author
3 ALPINES - Algorithms and parallel tools for integrated numerical simulations
Institut National des Sciences Mathématiques et de leurs Interactions, Inria de Paris, LJLL - Laboratoire Jacques-Louis Lions
Abstract : In this work, we consider conforming finite element discretizations of arbitrary polynomial degree $p ≥ 1$ of the Poisson problem. We propose a multilevel a posteriori estimator of the algebraic error. We prove that this estimator is reliable and efficient (represents a two-sided bound of the error), with a constant independent of the degree $p$. We next design a multilevel iterative algebraic solver from our estimator and we show that this solver contracts the algebraic error on each iteration by a factor bounded independently of $p$. Actually, we show that these two results are equivalent. The $p$-robustness results rely on the work of Schöberl et al. [IMA J. Numer. Anal., 28 (2008), pp. 1-24] for one given mesh. We combine this with the design of an algebraic residual lifting constructed over a hierarchy of nested, unstructured simplicial meshes, in the spirit of Papež et al. [HAL Preprint 01662944, 2017]. This includes a global coarse-level lowest-order solve, with local higher-order contributions from the subsequent mesh levels. These higher-order contributions are given as solutions of mutually independent Dirichlet problems posed over patches of elements around vertices. This residual lifting is the core of our a posteriori estimator and determines the descent direction for the next iteration of our multilevel solver. Its construction can be seen as one geometric V-cycle multigrid step with zero pre- and one post-smoothing by damped additive Schwarz. Numerical tests are presented to illustrate the theoretical findings.
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https://hal.archives-ouvertes.fr/hal-02070981
Contributor : Ani Miraçi <>
Submitted on : Monday, March 18, 2019 - 12:41:58 PM
Last modification on : Wednesday, May 15, 2019 - 3:39:28 AM

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• HAL Id : hal-02070981, version 1

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Ani Miraçi, Jan Papež, Martin Vohralík. A multilevel algebraic error estimator and the corresponding iterative solver with $p$-robust behavior. 2019. ⟨hal-02070981⟩

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