Finite operators and similarity orbits

Fialkow, Lawrence A.; Herrero, Domingo A.

doi:10.1090/S0002-9939-1985-0776187-X

Finite operators and similarity orbits
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by Lawrence A. Fialkow and Domingo A. Herrero PDF

Proc. Amer. Math. Soc. 93 (1985), 601-609 Request permission

Abstract:

In this note we answer the question of J. P. Williams as to which Hilbert space operators $T$ have the property that every similarity transformation ${W^{ - 1}}TW$ is a finite operator: $T$ has this property if and only if its image in the Calkin algebra satisfies a quadratic equation.

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