ALGEBRAIC DEGREE IN SPATIAL MATRICIAL NUMERICAL RANGES OF LINEAR OPERATORS
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Date
2021-07-20
Authors
Bernik, Janez
Livshits, Leo
MacDonald, Gordon W.
Marcoux, Laurent W.
Mastnak, Mitja
Radjavi, Heydar
Advisor
Journal Title
Journal ISSN
Volume Title
Publisher
American Mathematical Society
Abstract
We study the maximal algebraic degree of principal ortho-compressions of linear operators that constitute spatial matricial numerical ranges of higher order. We demonstrate (amongst other things) that for a (possibly unbounded) operator L on a Hilbert space, every principal m-dimensional ortho-compression of L has algebraic degree less than m if and only if rank(L − λI) ≤ m − 2 for some λ ∈ C
Description
First published in Proceedings of the American Mathematical Society in volume 149, issue 10 in 2021, published by the American Mathematical Society
Keywords
spatial matricial numerical ranges, algebraic degree, rank modulo scalars, orthogonal compressions, principal submatrices, cyclic matrices, non-derogatory matrices