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  1. Abstract

    Gradient‐type iterative methods for solving Hermitian eigenvalue problems can be accelerated by using preconditioning and deflation techniques. A preconditioned steepest descent iteration with implicit deflation (PSD‐id) is one of such methods. The convergence behavior of the PSD‐id is recently investigated based on the pioneering work of Samokish on the preconditioned steepest descent method (PSD). The resulting non‐asymptotic estimates indicate a superlinear convergence of the PSD‐id under strong assumptions on the initial guess. The present paper utilizes an alternative convergence analysis of the PSD by Neymeyr under much weaker assumptions. We embed Neymeyr's approach into the analysis of the PSD‐id using a restricted formulation of the PSD‐id. More importantly, we extend the new convergence analysis of the PSD‐id to a practically preferred block version of the PSD‐id, or BPSD‐id, and show the cluster robustness of the BPSD‐id. Numerical examples are provided to validate the theoretical estimates.

     
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    Free, publicly-accessible full text available October 1, 2024
  2. Abstract

    We consider the problem of extracting a few desired eigenpairs of the buckling eigenvalue problem , whereKis symmetric positive semi‐definite,KGis symmetric indefinite, and the pencil is singular, namely,KandKGshare a nontrivial common nullspace. Moreover, in practical buckling analysis of structures, bases for the nullspace ofKand the common nullspace ofKandKGare available. There are two open issues for developing an industrial strength shift‐invert Lanczos method: (1) the shift‐invert operator does not exist or is extremely ill‐conditioned, and (2) the use of the semi‐inner product induced byKdrives the Lanczos vectors rapidly toward the nullspace ofK, which leads to a rapid growth of the Lanczos vectors in norms and causes permanent loss of information and the failure of the method. In this paper, we address these two issues by proposing a generalized buckling spectral transformation of the singular pencil and a regularization of the inner product via a low‐rank updating of the semi‐positive definiteness ofK. The efficacy of our approach is demonstrated by numerical examples, including one from industrial buckling analysis.

     
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