The structure of the core of a numerical contraction |
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Authors: | T Hara |
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Institution: | (1) Department of Mathematics, Fukuoka University of Education, 811-41 Munakata, Fukuoka, Japan |
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Abstract: | A bounded linear operatorT is a numerical contraction if and only if there exists a selfadjoint contractionZ such that
. The aim of the present paper is to study the structure of the coreZ(T) of all selfadjoint contractions satisfying the above inequality. Especially we consider several conditions for thatZ(T) is a single-point set. By using this argument we shall characterize extreme points of the set of all numerical contractions. Moreover we shall give effective sufficient conditions for extreme points. |
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Keywords: | 47A12 15A60 |
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