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ETNA - Electronic Transactions on Numerical Analysis
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Verlag der Österreichischen Akademie der Wissenschaften Austrian Academy of Sciences Press
A-1011 Wien, Dr. Ignaz Seipel-Platz 2
Tel. +43-1-515 81/DW 3420, Fax +43-1-515 81/DW 3400 https://verlag.oeaw.ac.at, e-mail: verlag@oeaw.ac.at |
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DATUM, UNTERSCHRIFT / DATE, SIGNATURE
BANK AUSTRIA CREDITANSTALT, WIEN (IBAN AT04 1100 0006 2280 0100, BIC BKAUATWW), DEUTSCHE BANK MÜNCHEN (IBAN DE16 7007 0024 0238 8270 00, BIC DEUTDEDBMUC)
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ETNA - Electronic Transactions on Numerical Analysis, pp. 119-137, 2024/09/19
We consider iteration for approximately solving large-scale algebraic Sylvester equations. Inside every iteration step of this iterative process, a pair of linear systems of equations has to be solved. We investigate the situation when those inner linear systems are solved inexactly by an iterative method such as, for example, preconditioned Krylov subspace methods. The main contribution of this work are thresholds for the required accuracies regarding the inner linear systems, which dictate when the employed inner Krylov subspace methods can be safely terminated. The goal is to save computational effort by solving the inner linear system as inaccurately as possible without endangering the functionality of the low-rank Sylvester–ADI method. Ideally, the inexact ADI method mimics the convergence behavior of the more expensive exact ADI method, where the linear systems are solved directly. Alongside the theoretical results, strategies for an actual practical implementation of the stopping criteria are also developed. Numerical experiments confirm the effectiveness of the proposed strategies.
Keywords: Sylvester equation, alternating direction implicit, low-rank approximation, inner–outer methods