Jerry J. Koliha

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We study perturbations of the Drazin inverse of a closed linear operator A for the case when the perturbed operator has the same spectral projection as A. This theory subsumes results recently obtained by Wei and Wang, Rakočevi´c and Wei, and Castro and Koliha. We give explicit error estimates for the perturbation of Drazin inverse, and error estimates(More)
The paper solves a long standing problem of finding error bounds for a general perturbation of the Drazin inverse. The bounds are given in terms of the distance between the matrices together with the distance between their eigenprojections. Estimates using the gap between subspaces are also given. Recent results of several authors, including Castro, Koliha,(More)
We study perturbations and the continuity of the Drazin inverse of a closed linear operator A and obtain explicit error estimates in terms of the gap between closed operators and in terms of the gap between ranges and nullspaces of operators. The results are used to derive a theorem on the continuity of the Drazin inverse for closed operators and to(More)
We study semi-iterative methods for an approximate solution of a linear equation x = T x+c with a bounded linear operator T acting on a Banach space X, considering separately the cases when λ = 1 is an isolated and accumulation spectral point for T. We give necessary and sufficient conditions for the convergence of a semi-iterative method, utilizing the(More)
The paper deals with the generalized Drazin invertibility of combinations of idempotents p, q in a Banach algebra. It proves the equivalence of the generalized Drazin invertibility of p − q and p + q, as well as the equivalence of the generalized Drazin invertibility of the commutator pq − qp and anticommu-tator pq + qp of p, q. It extends several results(More)