scholarly journals ON RELATIVE ESSENTIAL SPECTRA OF BLOCK OPERATOR MATRICES AND APPLICATION

2016 ◽  
Vol 53 (3) ◽  
pp. 681-698 ◽  
Author(s):  
Salma Charfi ◽  
Ines Walha
Keyword(s):  
Operator Matrices ◽  
Essential Spectra ◽  
Block Operator ◽  
Block Operator Matrices

scholarly journals Perturbation theory, M-essential spectra of operator matrices

Filomat ◽  
2020 ◽  
Vol 34 (4) ◽  
pp. 1187-1196
Author(s):  
Boulbeba Abdelmoumen ◽  
Sonia Yengui
Keyword(s):  
Banach Space ◽  
Perturbation Theory ◽  
Banach Spaces ◽  
General Class ◽  
Operator Matrix ◽  
Operator Matrices ◽  
Essential Spectra ◽  
Block Operator Matrix ◽  
Block Operator ◽  
Block Operator Matrices

In this paper, we will establish some results on perturbation theory of block operator matrices acting on Xn, where X is a Banach space. These results are exploited to investigate the M-essential spectra of a general class of operators defined by a 3x3 block operator matrix acting on a product of Banach spaces X3.

Sharp Inequalities for the Numerical Radii of Block Operator Matrices

2019 ◽  
Vol 45 (4) ◽  
pp. 687-703
Author(s):  
M. Ghaderi Aghideh ◽  
M. S. Moslehian ◽  
J. Rooin
Keyword(s):  
Operator Matrices ◽  
Block Operator ◽  
Block Operator Matrices

scholarly journals Essential numerical ranges for linear operator pencils

2019 ◽  
Vol 40 (4) ◽  
pp. 2256-2308
Author(s):  
Sabine Bögli ◽  
Marco Marletta
Keyword(s):  
Linear Operator ◽  
Numerical Range ◽  
Projection Methods ◽  
Operator Pencil ◽  
Operator Matrices ◽  
New Concepts ◽  
Block Operator ◽  
Block Operator Matrices ◽  
Spectral Pollution ◽  
Operator Pencils

Abstract We introduce concepts of essential numerical range for the linear operator pencil $\lambda \mapsto A-\lambda B$. In contrast to the operator essential numerical range, the pencil essential numerical ranges are, in general, neither convex nor even connected. The new concepts allow us to describe the set of spectral pollution when approximating the operator pencil by projection and truncation methods. Moreover, by transforming the operator eigenvalue problem $Tx=\lambda x$ into the pencil problem $BTx=\lambda Bx$ for suitable choices of $B$, we can obtain nonconvex spectral enclosures for $T$ and, in the study of truncation and projection methods, confine spectral pollution to smaller sets than with hitherto known concepts. We apply the results to various block operator matrices. In particular, Theorem 4.12 presents substantial improvements over previously known results for Dirac operators while Theorem 4.5 excludes spectral pollution for a class of nonselfadjoint Schrödinger operators which has not been possible to treat with existing methods.

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