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Proceedings of the American Mathematical Society
Proceedings of the American Mathematical Society
ISSN 1088-6826(online) ISSN 0002-9939(print)

 

The numerical range and the essential numerical range


Author: J. P. Williams
Journal: Proc. Amer. Math. Soc. 66 (1977), 185-186
MSC: Primary 47A10
MathSciNet review: 0458203
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Abstract: A simple proof is given of Lancaster's theorem that the convex hull of the numerical and essential numerical ranges of a Hilbert space operator is the closure of the numerical range.


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Additional Information

DOI: http://dx.doi.org/10.1090/S0002-9939-1977-0458203-3
PII: S 0002-9939(1977)0458203-3
Keywords: Operator on Hilbert space, numerical range, essential numerical range
Article copyright: © Copyright 1977 American Mathematical Society