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We study the norm derivatives in the context of Birkhoff-James orthogonality in real Banach spaces. As an application of this, we obtain a complete characterization of the left-symmetric points and the right-symmetric points in a real…

Functional Analysis · Mathematics 2020-09-25 Divya Khurana , Debmalya Sain

We study best approximations in Banach spaces via Birkhoff-James orthogonality of functionals. To exhibit the usefulness of Birkhoff-James orthogonality techniques in the study of best approximation problems, some algorithms and distance…

Functional Analysis · Mathematics 2021-04-30 Debmalya Sain , Saikat Roy

There are two notions of approximate Birkhoff-James orthogonality in a normed space. We characterize both the notions of approximate Birkhoff-James orthogonality in the space of bounded linear operators defined on a normed space. A complete…

Functional Analysis · Mathematics 2024-08-13 Kallol Paul , Debmalya Sain , Arpita Mal

Two different notions of approximate Birkhoff-James orthogonality in nor\-med linear spaces have been introduced by Dragomir and Chmie\-li\'n\-ski. In the present paper we consider a global and a local approximate symmetry of the…

Functional Analysis · Mathematics 2020-12-16 Jacek Chmieliński , Divya Khurana , Debmalya Sain

We study two notions of approximate Birkhoff-James orthogonality in a normed space, from a geometric point of view, and characterize them in terms of normal cones. We further explore the interconnection between normal cones and approximate…

Functional Analysis · Mathematics 2024-07-30 Debmalya Sain , Kallol Paul , Arpita mal

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

It is shown that Birkhoff-James orthogonality knows everything about the smooth norms in reflexive Banach spaces and can also compute the dimensions of the underlying normed spaces.

Functional Analysis · Mathematics 2021-09-21 Ljiljana Arambašić , Alexander Guterman , Bojan Kuzma , Rajna Rajić , Svetlana Zhilina

This paper deals with study of Birkhoff-James orthogonality of a linear operator to a subspace of operators defined between arbitrary Banach spaces. In case the domain space is reflexive and the subspace is finite dimensional we obtain a…

Functional Analysis · Mathematics 2019-12-10 Arpita Mal , Kallol Paul

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 extend the investigations regarding Birkhoff-James orthogonality of linear operators to bounded continuous functions on metric spaces. We introduce Birkhoff-James extensions of continuous functions and study them in…

Functional Analysis · Mathematics 2021-08-31 Saptak Bhattacharya

We study the concepts of orthogonality and smoothness in normed linear spaces, induced by the derivatives of the norm function. We obtain analytic characterizations of the said orthogonality relations in terms of support functionals in the…

Functional Analysis · Mathematics 2024-08-02 Debmalya Sain

In this paper, we study Birkhoff-James orthogonality of bounded linear operators and give a complete characterization of Birkhoff-James orthogonality of bounded linear operators on infinite dimensional real normed linear spaces. As an…

Functional Analysis · Mathematics 2024-08-13 Debmalya Sain , Kallol Paul , Arpita Mal

We study the smoothness and the norm attainment of bounded bilinear operators between Banach spaces, using the concepts of Birkhoff-James orthogonality and semi-inner-products. In the finite-dimensional case, we characterize Birkhoff-James…

Functional Analysis · Mathematics 2019-07-04 Debmalya Sain

We find expressions for the Gateaux derivative of the matrix norms in operator spaces, and operator systems. Some applications of the results to quantum probability measures, states on C$^*$-algebras, and Birkhoff-James orthogonality are…

Operator Algebras · Mathematics 2025-10-07 Sushil Singla

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

In this article, the relationship between Birkhoff-James orthogonality of elementary tensors in certain tensor product spaces with the Birkhoff-James orthogonality of individual elements in their respective spaces is studied.

Functional Analysis · Mathematics 2022-10-26 Mohit , Ranjana Jain

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 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

We use Birkhoff-James' orthogonality in Banach spaces to provide new conditions for the converse of the classical Riesz's representation theorem.

Functional Analysis · Mathematics 2013-09-18 V. Capraro , S. Rossi

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
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