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We introduce the notion of approximate smoothness in a normed linear space. We characterize this property and show the connections between smoothness and approximate smoothness for some spaces. As an application, we consider in particular…

Functional Analysis · Mathematics 2022-11-08 Jacek Chmieliński , Divya Khurana , Debmalya Sain

We completely characterize Birkhoff-James orthogonality with respect to numerical radius norm in the space of bounded linear operators on a complex Hilbert space. As applications of the results obtained, we estimate lower bounds of…

Functional Analysis · Mathematics 2024-08-13 Arpita Mal , Kallol Paul , Jeet Sen

In this article, we discuss the relationship between Birkhoff-James orthogonality of elementary tensors in the space $L^{p}(\mu)\otimes^{\Delta_{p}}X,\; (1\leq p<\infty)$ with the individual elements in their respective spaces, where $X$ is…

Functional Analysis · Mathematics 2023-10-31 Mohit , Ranjana Jain

We study Birkhoff-James orthogonality and isosceles orthogonality of bounded linear operators between Hilbert spaces and Banach spaces. We explore Birkhoff-James orthogonality of bounded linear operators in light of a new notion introduced…

Functional Analysis · Mathematics 2020-04-28 Tamara Bottazzi , Cristian Conde , Debmalya Sain

We characterize Birkhoff-James orthogonality of continuous vector-valued functions on a compact topological space. As an application of our investigation, Birkhoff-James orthogonality of real bilinear forms are studied. This allows us to…

Functional Analysis · Mathematics 2024-07-19 Saikat Roy , Tanusri Senapati , Debmalya Sain

The main aim of this paper is to provide characterizations of Birkhoff-James orthogonality (BJ-orthogonality in short) in a number of families of Banach spaces in terms of the elements of significant subsets of the unit ball of their dual…

Functional Analysis · Mathematics 2024-02-05 Miguel Martin , Javier Meri , Alicia Quero , Saikat Roy , Debmalya Sain

In this paper we study Birkhoff-James Orthogonality for biadjoints of operators. We partly solve the problem, if an operator is orthogonal to the space of operators valued in a subspace, when the is the norm of biadjoint is attained at a…

Functional Analysis · Mathematics 2022-12-13 Taduri Srinivasa Siva Rama Krishna Rao

We classify real or complex finite-dimensional $C^*$-algebras and their underlying fields from the properties of Birkhoff-James orthogonality. Application to strong Birkhoff-James orthogonality preservers is also given.

Operator Algebras · Mathematics 2024-11-26 Bojan Kuzma , Sushil Singla

We observe that the classical notion of numerical radius gives rise to a notion of smoothness in the space of bounded linear operators on certain Banach spaces, whenever the numerical radius is a norm. We demonstrate an important class of…

Functional Analysis · Mathematics 2021-07-09 Saikat Roy , Debmalya Sain

In this paper, we obtain some characterizations of the (strong) Birkhoff--James orthogonality for elements of Hilbert $C^*$-modules and certain elements of $\mathbb{B}(\mathscr{H})$. Moreover, we obtain a kind of Pythagorean relation for…

Operator Algebras · Mathematics 2021-07-23 Mohammad Sal Moslehian , Ali Zamani

We classify bijective maps which strongly preserve Birkhoff-James orthogonality on a finite-dimensional complex $C^*$-algebra. It is shown that those maps are close to being real-linear isometries whose structure is also determined.

Operator Algebras · Mathematics 2025-02-13 Bojan Kuzma , Srdjan Stefanović

In this article we study the difference between orthogonality induced by the norm derivatives (known as $\rho$-orthogonality) and Birkhoff-James orthogonality in a normed linear space $ \mathbb X$ by introducing a new geometric constant,…

Functional Analysis · Mathematics 2024-12-24 Souvik Ghosh , Kallol Paul , Debmalya Sain

We study the relationship between the point-wise symmetry of Birkhoff-James orthogonality and the geometry of the space of operators $\mathbb{B}(\ell_\infty^n,\ell_1^m)$. We show that any non-zero left-symmetric point in this space is a…

Functional Analysis · Mathematics 2022-11-17 Babhrubahan Bose

We study left symmetric bounded linear operators in the sense of Birkhoff-James orthogonality defined between infinite dimensional Banach spaces. We prove that a bounded linear operator defined between two strictly convex Banach spaces is…

Functional Analysis · Mathematics 2024-08-13 Kallol Paul , Arpita Mal , Pawel Wójcik

In this paper we characterize Birkhoff-James orthogonality of linear operators defined on a finite dimensional real Banach space $ \mathbb{X}. $ We also explore the symmetry of Birkhoff-James orthogonality of linear operators defined on $…

Functional Analysis · Mathematics 2016-07-29 Debmalya Sain

We study approximate Birkhoff-James orthogonality of bounded linear operators defined between normed linear spaces $\mathbb{X}$ and $\mathbb{Y}.$ As an application of the results obtained, we characterize smoothness of a bounded linear…

Functional Analysis · Mathematics 2024-08-13 Arpita Mal , Kallol Paul , T. S. S. R. K. Rao , Debmalya Sain

We introduce the notion of orthogonality in a vector space with a topology on it. To serve our purpose, we define orthogonality space for a given vector space X, using the topology on it. We show that for a suitable choice of orthogonality…

Functional Analysis · Mathematics 2019-10-28 Debmalya Sain , Saikat Roy , Kallol Paul

We completely characterize the left-symmetric points, the right-symmetric points, and, the symmetric points in the sense of Birkhoff-James, in a Banach space. We obtain a complete characterization of the left-symmetric (right-symmetric)…

Functional Analysis · Mathematics 2019-09-30 Debmalya Sain , Saikat Roy , Satya Bagchi , Vitor Balestro

We identify the smooth points of $L^1(\mu,X)$, and provide some necessary and sufficient conditions for left and right symmetry of points with respect to Birkhoff-James orthogonality in $L^p(\mu,X), 1\leq p<\infty$, where $\mu$ is any…

Functional Analysis · Mathematics 2025-04-07 Mohit , Ranjana Jain

We study the concepts of Birkhoff--James orthogonality and parallelism in Hilbert space operators, induced by the operator radius norm $w_{\rho}(\cdot)$. In particular, we completely characterize Birkhoff--James orthogonality and…

Functional Analysis · Mathematics 2024-05-14 Fuad Kittaneh , Ali Zamani