Open AccessThe numerical range of linear operators
Author(s) -
Salah Mecheri
Publication year - 2008
Publication title -
filomat
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.449
H-Index - 34
eISSN - 2406-0933
pISSN - 0354-5180
DOI - 10.2298/fil0802001m
Subject(s) - mathematics , numerical range , range (aeronautics) , linear operators , mathematical analysis , materials science , composite material , bounded function
In (27) J.P.Williams showed that an operator A 2 B(H) is normaloid if and only if it is convexoid. It is known that the part if in J.P.William's result is not true as it mentioned in the review MR0264445. In this paper we will present an example which contractics the part " if " in J.P. williams' result. We also give a simple proof of the part "only if" of this result. A necessary and sucient condition for an operator A 2 B(H) to be convexoid is also given.
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