Results 31 to 40 of about 513 (80)
Generalized Derivations and Norm Equality in Normed Ideals [PDF]
, 2011 2000 Mathematics Subject Classification: 47A10, 47A12, 47A30, 47B10, 47B20, 47B37, 47B47, 47D50.We compare the norm of a generalized derivation on a Hilbert space with the norm of its restrictions to Schatten norm ...
Barraa, Mohamed
core
Continuity properties of vectors realizing points in the classical field of values [PDF]
, 2013 For an $n$-by-$n$ matrix $A$, let $f_A$ be its "field of values generating function" defined as $f_A\colon x\mapsto x^*Ax$. We consider two natural versions of the continuity, which we call strong and weak, of $f_A^{-1}$ (which is of course multi-valued)
Corey, Dan +4 more
core +3 more sources
Numerical radius inequalities associated with the Cartesian decomposition
, 2015 We give several sharp numerical radius inequalities associated with the Cartesian decomposition of a Hilbert space operator A = B + iC . Among other inequalities, it is shown that 1 2 ‖ |B| + |C|‖ wr(A) ‖ |B| + |C|‖ for 0 < r 2 , where w(·) and ...
F. Kittaneh
semanticscholar +1 more source
Scalar approximants of quadratic operators with applications
, 2018 Among other results, we find the best scalar approximant of a quadratic operator with respect to the numerical radius and the operator norm. We use these results to give estimates for the numerical radii of products and commutators of quadratic operators.
A. Abu-Omar, P. Wu
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Domaine Numérique du produit AB avec A normal [PDF]
, 2006 2000 Mathematics Subject Classification: 18B30, 47A12.Let A, B be two linear operators on a complex Hilbert space H. We extend a Bouldin's result (1969) conserning W(AB) - the numerical range of the product AB. We show, when AB = BA and A is normal, than
Kaadoud, Mohamed Chraïbi
core
The joint essential numerical range of operators: convexity and related results
, 2009 LetW (A) andWe(A) be the joint numerical range and the joint essential numerical range of an m-tuple of self-adjoint operators A = (A1, . . . , Am) acting on an infinite dimensional Hilbert space, respectively.
Chi-Kwong Li, Y. Poon
semanticscholar +1 more source
Convexity around the Unit of a Banach Algebra [PDF]
, 2008 2000 Mathematics Subject Classification: Primary: 46B20. Secondary: 46H99, 47A12.We estimate the (midpoint) modulus of convexity at the unit 1 of a Banach algebra A showing that inf {max±||1 ± x|| − 1 : x ∈ A, ||x||=ε} ≥ (π/4e)ε²+o(ε²) as ε → 0. We also
Kadets, Vladimir +3 more
core
A fiedler-type theorem for the determinant of J-positive matrices
, 2016 In this note we characterize the set of all possible values attained by the determinant of the sum of two J -positive matrices with prescribed spectra, under a natural compatibility condition. Mathematics subject classification (2010): 46C20, 47A12.
N. Bebiano, J. Providência
semanticscholar +1 more source
Remarks on the Crouzeix-Palencia proof that the numerical range is a $(1+\sqrt2)$-spectral set
, 2018 Crouzeix and Palencia recently showed that the numerical range of a Hilbert-space operator is a $(1+\sqrt2)$-spectral set for the operator. One of the principal ingredients of their proof can be formulated as an abstract functional-analysis lemma.
Ransford, Thomas, Schwenninger, Felix
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On the block numerical range of operators on arbitrary Banach spaces
, 2018 We investigate the block numerical range of bounded linear operators on arbitrary Banach spaces. We show that the spectrum of an operator is always contained in the closure of its block numerical range.
Agnes Radl, M. Wolff
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