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In this paper, we study the descriptive complexity of some inevitable classes of Banach spaces. Precisely, as shown in [Go], every Banach space either contains a hereditarily indecomposable subspace or an unconditional basis, and, as shown…

Functional Analysis · Mathematics 2016-12-23 Bruno de Mendonça Braga

For a certain class of algebras $\cal A$ we give a method for constructing Banach spaces $X$ such that every operator on $X$ is close to an operator in $\cal A$. This is used to produce spaces with a small amount of structure. We present…

Functional Analysis · Mathematics 2008-09-01 W. T. Gowers , B. Maurey

We review recent work connected with the invariant subspace problem for operators, in particular new developments in the last 15 years. In particular, we include discussions of almost-invariant subspaces, universal operators, specific…

Functional Analysis · Mathematics 2025-07-30 I. Chalendar , J. R. Partington

We verify that a large portion of the theory of complex operator spaces and operator algebras (as represented by the 2004 book by the author and Le Merdy for specificity) transfers to the real case. We point out some of the results that do…

Operator Algebras · Mathematics 2024-05-03 David P. Blecher

It has been very recently discovered that there are compact linear operators between Banach spaces which cannot be approximated by norm attaining operators. The aim of this expository paper is to give an overview of those examples and also…

Functional Analysis · Mathematics 2017-04-25 Miguel Martin

We show that the main problem left open in Wenzel: "Real and complex operator ideals" (wenzelopidls.latex), can be solved using the Banach spaces $Z_\alpha$ recently constructed by Kalton: "An elementary example of a Banach space not…

Functional Analysis · Mathematics 2016-09-07 Joerg Wenzel

Necessary and sufficient conditions for a separable Banach space to be a dual space are proved. Some applications are discussed

Functional Analysis · Mathematics 2010-03-12 Stefano Rossi

In this paper we prove coincidence results concerning spaces of absolutely summing multilinear mappings between Banach spaces. The nature of these results arises from two distinct approaches: the coincidence of two \textit{a priori}…

Functional Analysis · Mathematics 2014-04-07 Oscar Blasco , Geraldo Botelho , Daniel Pellegrino , Pilar Rueda

Real and complex norms of a linear operator acting on a normed complexified space are considered. Bounds on the ratio of these norms are given. The real and complex norms are shown to coincide for four classes of operators: 1) real linear…

Functional Analysis · Mathematics 2007-05-23 Olga Holtz , Michael Karow

We consider the problem of solving a linear system of equations which involves complex variables and their conjugates. We characterize when it reduces to a complex linear system, that is, a system involving only complex variables (and not…

Rings and Algebras · Mathematics 2017-06-02 Cédric Josz

The paper is devoted to obtaining conditions for the roughness of dichotomy in the Banach spaces. Deep analysis of the well known papers was considered. The main results also works for the case of unbounded operators.

Dynamical Systems · Mathematics 2023-09-06 O. Iskra , S. Dashkovskiy , A. Pokutniy , V. Slynko , Yu. Zahorulko

We introduce the operators "modified limit" and "accumulation" on a Banach space, and we use this to define what we mean by being internally computable over the space. We prove that any externally computable function from a computable…

Logic · Mathematics 2015-07-01 Dag Normann

We present an overview to the approximation property, paying especial attention to the recent results relating the approximation property to ideals of linear operators and Lipschitz ideals. We complete the paper with some new results on…

Functional Analysis · Mathematics 2016-09-12 Pilar Rueda , Enrique A. Sanchez-Perez

In this article, we give a representation for compact operators acting between reflexive Banach spaces, which generalizes the representation given by Edmunds et al. for compact operators between reflexive Banach spaces with strictly convex…

Functional Analysis · Mathematics 2023-08-16 G. Ramesh , M. Veena Sangeetha , Shanola S. Sequeira

We show that some previous results concerning the boundedness of differentiation and integration operators on weighted spaces given by radial weights in the unit disk or the complex plane might fail without some natural additional…

Functional Analysis · Mathematics 2016-04-04 Alexander V. Abanin , Pham Trong Tien

In this paper we completely characterize the norm attainment set of a bounded linear operator on a Hilbert space. This partially answers a question raised recently in [\textit{D. Sain, On the norm attainment set of a bounded linear…

Functional Analysis · Mathematics 2019-03-20 Debmalya Sain

In this paper we investigate some dichotomy concepts for linear difference equations in Banach spaces. We motivate our approach by illustrative examples.

Dynamical Systems · Mathematics 2011-08-26 Ioan-Lucian Popa , Mihail Megan , Traian Ceausu

A topological setting is defined to study the complexities of the relation of equivalence of embeddings (or "position") of a Banach space into another and of the relation of isomorphism of complex structures on a real Banach space. The…

Functional Analysis · Mathematics 2017-01-17 Razvan Anisca , Valentin Ferenczi , Yolanda Moreno

For a bounded linear operator on a Banach space, we study approximation of the spectrum and pseudospectra in the Hausdorff distance. We give sufficient and necessary conditions in terms of pointwise convergence of appropriate spectral…

Functional Analysis · Mathematics 2022-09-12 Marko Lindner , Dennis Schmeckpeper

We explore the relation between lattice versions of strict singularity for operators from a Banach lattice to a Banach space. In particular, we study when the class of disjointly strictly singular operators, those not invertible on the span…

Functional Analysis · Mathematics 2014-10-20 Julio Flores , Jordi López-Abad , Pedro Tradacete