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Browsing by Subject "essential numerical range"

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  • thumbnail.journal.alt
    Item type:Article, Access status: Open Access ,
    Hilderbrand's theorem for the essential spectrum
    (2015) Bračič, Janko; Diogo, Cristina
    We prove a variant of Hildebrandt’s theorem which asserts that the convex hull of the essential spectrum of an operator $A$ on a complex Hilbert space is equal to the intersection of the essential numerical ranges of operators which are similar to $A$. As a consequence, it is given a necessary and sufficient condition for zero not being in the convex hull of the essential spectrum of $A$.