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An improvement of the author's result, proved in 1961, concerning necessary and sufficient conditions for the compactness of embedding operators is given. A counterexample to a published statement concerning compactness of embedding…

Numerical Analysis · Mathematics 2007-05-23 A. G. Ramm

We establish a new $T1$ theorem for the compactness of bi-parameter Calder\'on-Zygmund singular integral operators. Namely, we show that if a bi-parameter CZO $T$ satisfies the product weak compactness property, the mixed weak…

Classical Analysis and ODEs · Mathematics 2026-01-12 Cody B. Stockdale , Cody Waters

The powerful concept of an operator ideal on the class of all Banach spaces makes sense in the real and in the complex case. In both settings we may, for example, consider compact, nuclear, or $2$--summing operators, where the definitions…

Functional Analysis · Mathematics 2016-09-06 Joerg Wenzel

Andreu et al [2] and Sadovskii [11] used representation spaces to study measures of non-compactness and spectral radii of operators on Banach lattices. In this paper, we develop representation spaces based on the nonstandard hull…

Functional Analysis · Mathematics 2007-05-23 Vladimir G. Troitsky

Given a set $B$ of operators between subspaces of $L_p$ spaces, we characterize the operators between subspaces of $L_p$ spaces that remain bounded on the $X$-valued $L_p$ space for every Banach space on which elements of the original class…

Functional Analysis · Mathematics 2021-03-10 Mikael de la Salle

The Rubio de Francia extrapolation theorem is a very powerful result which states that in order to show that certain operators satisfy weighted norm inequalities with Muckenhoupt weights it suffices to see that the corresponding…

Analysis of PDEs · Mathematics 2023-08-30 José María Martell , Pierre Portal

In this paper we characterize some basic properties of composition operators on the spaces of harmonic Bloch functions. First we provide some equivalent conditions for boundedness and compactness of composition operators. Then by using…

Functional Analysis · Mathematics 2018-12-27 Y. Estaremi , S. Esmaili , A. Ebadian

In this paper, using generalized metric projection, we propose a new extragradient method for finding a common element of the solutions set of a generalized equilibrium problem and a variational inequality for an $\alpha$-inverse-strongly…

Functional Analysis · Mathematics 2016-11-01 Zeynab Jouymandi , Fridoun Moradlou

We propose two very simple methods, the first one with constant step sizes and the second one with self-adaptive step sizes, for finding a zero of the sum of two monotone operators in real reflexive Banach spaces. Our methods require only…

Optimization and Control · Mathematics 2022-07-12 Chinedu Izuchukwu , Simeon Reich , Yekini Shehu

In this paper, we will study some properties of b-weakly compact operators and we will investigate their relationships to some variety of operators on the normed vector lattices. With some new conditions, we show that the modulus of an…

Functional Analysis · Mathematics 2019-05-28 Kazem Haghnejad Azar

We show that if the Hardy-Littlewood maximal operator is bounded on a reflexive Banach function space $X(\mathbb{R})$ and on its associate space $X'(\mathbb{R})$, then the space $X(\mathbb{R})$ has an unconditional wavelet basis. As a…

Functional Analysis · Mathematics 2019-08-22 Cláudio A. Fernandes , Alexei Yu. Karlovich , Yuri I. Karlovich

The worst-case performance of an optimization method on a problem class can be analyzed using a finite description of the problem class, known as interpolation conditions. In this work, we study interpolation conditions for linear operators…

Optimization and Control · Mathematics 2025-11-21 Nizar Bousselmi , Zhicheng Deng , Jie Lu , Francois Glineur , Julien M. Hendrickx

Let $A$ and $B$ be sectorial operators in a Banach space $X$ of angles $\omega_A$ and $\omega_B$, respectively, where $\omega_A+\omega_B<\pi$. We present a simple and common approach to results on closedness of the operator sum $A+B$, based…

Functional Analysis · Mathematics 2025-12-25 Bernhard H. Haak , Peer Christian Kunstmann

A linear operator $U$ acting boundedly on an infinite-dimensional separable complex Hilbert space $H$ is universal if every linear bounded operator acting on $H$ is similar to a scalar multiple of a restriction of $U$ to one of its…

Functional Analysis · Mathematics 2024-06-05 Luciano Abadías , F. Javier González-Doña , Jesús Oliva-Maza

The Van Leer approach for the approximation of nonlinear scalar conservation laws is studied in one space dimension. The problem can be reduced to a nonlinear interpolation and we propose a convexity property for the interpolated values. We…

Numerical Analysis · Mathematics 2010-07-28 François Dubois

Following ideas from the Abstract Interpolation Problem of Katsnelson et al. (Operators in spaces of functions and problems in function theory, vol 146, pp 83-69, Naukova Dumka, Keiv, 1987) for Schur class functions, we study a general…

Functional Analysis · Mathematics 2018-04-24 Joseph A. Ball , Vladimir Bolotnikov , Sanne ter Horst

A branch of generalizations of the Banach Fixed Point Theorem replaces contractivity by a weaker but still effective property. The aim of the present note is to extend the contraction principle in this spirit for such complete semimetric…

Functional Analysis · Mathematics 2017-06-29 Mihály Bessenyei , Zsolt Páles

We give orthonormal characterizations of collectively compact (limited) sets of linear operators from a Hilbert space to a Banach space.

Functional Analysis · Mathematics 2024-07-04 Svetlana Gorokhova

We show that the space of bounded and linear operators between spaces of continuous functions on compact Hausdorff topological spaces has the Bishop-Phelps-Bollob\'as property. A similar result is also proved for the class of compact…

The Rademacher series in rearrangement invariant function spaces "closed" to the space L_\infty are considered. In terms of interpolation theory of operators a correspondence between such spaces and spaces of coefficients generated by them…

Functional Analysis · Mathematics 2007-05-23 S. V. Astashkin