The spectrum of a selfadjoint compression of a self-adjoint operator.

Hosack, John M.

doi:10.1090/S0002-9939-1970-0271760-9

The spectrum of a selfadjoint compression of a self-adjoint operator.

Author: John M. Hosack
Journal: Proc. Amer. Math. Soc. 25 (1970), 83-85
MSC: Primary 47.30
DOI: https://doi.org/10.1090/S0002-9939-1970-0271760-9
MathSciNet review: 0271760
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Abstract: The relation between the spectrum of a selfadjoint operator and the spectrum of its compression is investigated. In particular, we show that the compression of a selfadjoint operator is essentially selfadjoint if and only if the spectrum of the closure of the compression is contained in the closed convex hull of the spectrum of the operator. Relations between two conceptions of compressions or projections of operators are also considered.

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