Abstract
A general argument is developed in order to construct approximants (and to obtain concrete expressions for the distance) for a given Hilbert space operator in a set of operators invariant under similarities and under compact perturbations. Several examples illustrate the main result.
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Herrero, D.A. The distance to a similarity-invariant set of operators. Integr equ oper theory 5, 131–140 (1982). https://doi.org/10.1007/BF01694034
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DOI: https://doi.org/10.1007/BF01694034