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A Generalization of the Multishift QR Algorithm
Author(s) -
Raf Vandebril,
David S. Watkins
Publication year - 2012
Publication title -
siam journal on matrix analysis and applications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.268
H-Index - 101
eISSN - 1095-7162
pISSN - 0895-4798
DOI - 10.1137/11085219x
Subject(s) - krylov subspace , mathematics , linear subspace , qr decomposition , convergence (economics) , generalization , algorithm , symbolic convergence theory , inverse , algebra over a field , eigenvalues and eigenvectors , iterative method , computer science , pure mathematics , key (lock) , mathematical analysis , physics , computer security , geometry , quantum mechanics , economics , economic growth
Recently a generalization of Francis’s implicitly shifted QR-algorithm was proposed, notably widening the class of matrices admitting low-cost implicit QR-steps. This unifying framework covered the methods and theory for Hessenberg and inverse Hessenberg matrices and furnished also new, single-shifted, QR-type methods for, e.g., CMV -matrices. Convergence of this approach was only suggested by numerical experiments. No theoretical claims supporting the results were presented. In this paper we present multishift variants of these new algorithms. We also provide a convergence theory that shows that the new algorithm performs nested subspace iterations on rational Krylov subspaces. Numerical experiments confirm the validity of the theory.status: publishe

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