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This short but self-contained survey presents a number of elegant matrix/operator inequalities for general convex or concave functions, obtained with a unitary orbit technique. Jensen, sub or super-additivity type inequalities are…

Functional Analysis · Mathematics 2014-02-26 Jean-Christophe Bourin , Eun-Young Lee

Let $\big(\mathcal{H}, \langle \cdot\mid \cdot\rangle \big)$ be a complex Hilbert space and $A$ be a positive (semidefinite) bounded linear operator on $\mathcal{H}$. The semi-inner product induced by $A$ is given by ${\langle x\mid…

Functional Analysis · Mathematics 2020-05-12 Kais Feki

In this paper, we improve and generalize the operator versions of Kantorovich and Wielandt inequalities for positive linear maps on Hilbert space. Our results are more extensive and precise than many previous results due to Fu and He…

Functional Analysis · Mathematics 2015-01-14 Wenshi Liao , Junliang Wu

We establish several operator extensions of the Chebyshev inequality. The main version deals with the Hadamard product of Hilbert space operators. More precisely, we prove that if $\mathscr{A}$ is a $C^*$-algebra, $T$ is a compact Hausdorff…

Functional Analysis · Mathematics 2014-05-30 Mohammad Sal Moslehian , Mojtaba Bakherad

The main goal of this article is to establish several new upper and lower bounds for the $\mathbb{A}$-numerical radius of $2\times 2$ operator matrices, where $\mathbb{A}$ be the $2\times 2$ diagonal operator matrix whose diagonal entries…

Functional Analysis · Mathematics 2020-07-08 Satyajit Sahoo

We obtain several sharp lower and upper bounds for the Euclidean operator radius of a pair of bounded linear operators defined on a complex Hilbert space. As applications of these bounds we deduce a chain of new bounds for the classical…

Functional Analysis · Mathematics 2024-08-14 Suvendu Jana , Pintu Bhunia , Kallol Paul

In this paper we study various forms of the Hardy inequality for Dunkl operators, including the classical inequality, $L^p$ inequalities, an improved Hardy inequality, as well as the Rellich inequality and a special case of the…

Functional Analysis · Mathematics 2020-06-22 Andrei Velicu

We prove that for a right linear bounded normal operator on a quaternionic Hilbert space (quaternionic bounded normal operator) the norm and the numerical radius are equal. As a consequence of this result we give a new proof of the known…

Spectral Theory · Mathematics 2016-10-04 G Ramesh

In this paper, by using the rotation method, we calculate that the sharp bound for $n$-dimensional Hardy operator $\mathcal{H}$ on mixed radial-angular spaces. Furthermore, we also obtain the sharp bound for $n$-dimensional fractional Hardy…

Classical Analysis and ODEs · Mathematics 2022-08-01 Mingquan Wei , Dunyan Yan

Some inequalities of Cauchy-Bunyakovsky-Schwarz type for sequences of bounded linear operators in Hilbert spaces and some applications are given.

Operator Algebras · Mathematics 2007-05-23 Sever Silvestru Dragomir

We introduce a new seminorm of $n$-tuple operators, which generalizes the $A$-Euclidean operator radius of $n$-tuple bounded linear operators on a complex Hilbert space. We introduce and study basic properties of this seminorm. As an…

Functional Analysis · Mathematics 2025-07-01 Pintu Bhunia , Messaoud Guesba

We use (versions of) the von Neumann inequality for Hilbert space contractions to prove several Schwarz-Pick inequalities. Specifically, we derive an alternate proof for a multi-point Schwarz-Pick inequality by Beardon and Minda, along with…

Functional Analysis · Mathematics 2024-07-19 Catalin Badea , Axel Renard

We completely characterize the Crawford number attainment set and the numerical radius attainment set of a bounded linear operator on a Hilbert space. We study the intersection properties of the corresponding attainment sets of numerical…

Functional Analysis · Mathematics 2020-01-28 Debmalya Sain , Arpita Mal , Pintu Bhunia , Kallol Paul

In this paper, we present various inequalities for generalized numerical radius of $2 \times 2$ block matrices for Schatten p-norm. Moreover, we give a refinement of the triangle inequality for the Schatten p-generalized numerical radius.

Functional Analysis · Mathematics 2022-04-07 Jana Hamza , Hassan Issa

In this paper, we derive a generalized multiplicative Hardy-Littlewood-Polya type inequality, as well as several related additive inequalities, for functions of operators in Hilbert spaces. In addition, we find the modulus of continuity of…

Functional Analysis · Mathematics 2015-10-06 Vladyslav Babenko , Yuliya Babenko , Nadiia Kriachko

In this paper, a generalized Cauchy-Schwarz inequality for positive sesquilinear maps with values in noncommutative Lp-spaces for p > 1 are obtained. Bound estimates for their real and imaginary parts are also provided, and, as an…

Operator Algebras · Mathematics 2026-02-13 Giorgia Bellomonte , Stefan Ivkovic , Camillo Trapani

We prove an inequality of Hardy type for functions in Triebel-Lizorkin spaces. The distance involved is being measured to a given Ahlfors d-regular set in R^n, with n-1<d<n. As an application of the Hardy inequality, we consider boundedness…

Classical Analysis and ODEs · Mathematics 2012-09-27 Lizaveta Ihnatsyeva , Antti V. Vähäkangas

We investigate some aspects of various numerical radius orthogonalities and numerical radius parallelism for bounded linear operators on a Hilbert space $\mathscr{H}$. Among several results, we show that if $T,S\in \mathbb{B}(\mathscr{H})$…

Functional Analysis · Mathematics 2020-04-07 Maryam Torabian , Maryam Amyari , Marzieh Moradian Khibary

We introduce compactness classes of Hilbert space operators by grouping together all operators for which the associated singular values decay at a certain speed and establish upper bounds for the norm of the resolvent of operators belonging…

Spectral Theory · Mathematics 2020-05-29 Ayse Guven , Oscar F. Bandtlow

We generalize several inequalities involving powers of the numerical radius for off-diagonal part of $2\times2$ operator matrices of the form $T=\left[\begin{array}{cc} 0&B, C&0 \end{array}\right]$, where $B, C$ are two operators. In…

Functional Analysis · Mathematics 2017-06-19 Monire Hajmohamadi , Rahmatollah Lashkaripour , Mojtaba Bakherad