Olavi Nevanlinna

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Restarted GMRES is known to be inefficient for solving shifted systems when the shifts are handled simultaneously. Variants have been proposed to enhance its performance. We show that another restarted method, restarted Full Orthogonaliza-tion Method (FOM), can effectively be employed. The total number of iterations of restarted FOM applied to all shifted(More)
We discuss computing the spectrum of a bounded operator and representing its resolvent operator. The results include a general convergence theorem for the polynomial convex hull of the spectrum and explicit representations for the resolvent outside. The results are formulated and proved in general Banach algebras. AMS subject classifications: 47A10, 47A12,(More)