Kais Feki

activity

20192024

most cited

A

-Numerical radius orthogonality and parallelism of semi-Hilbertian space operators and their applications

60 citations · 90 across the 14 of their papers we have counts for

collaborators

18 papers

math.FA2024

Joint $q$ -Numerical Ranges of Operators in Hilbert and Semi-Hilbert Spaces

Kais Feki, Arnab Patra, Jyoti Rani +1

This paper introduces and investigates the concept of the $q$ -numerical range for tuples of bounded linear operators in Hilbert spaces. We establish various inequalities concerning…

math.FA2023

On approximate $A$ -seminorm and $A$ -numerical radius orthogonality of operators

Cristian Conde, Kais Feki

This paper explores the concept of approximate Birkhoff-James orthogonality in the context of operators on semi-Hilbert spaces. These spaces are generated by positive semi-definite…

math.FA2023

A note on the generalized maximal numerical range of operators

Abderrahim Baghdad, El Hassan Benabdi, Kais Feki

The paper considers some new properties of the so-called $A$ -maximal numerical range of operators, denoted by $W_{m a x}^{A} (\cdot)$ , where $A$ is a positive bounded linear operator a…

math.FA2021★ 12 cited

Generalized $A$ -numerical radius of operators and related inequalities

Pintu Bhunia, Kais Feki, Kallol Paul

Let $A$ be a non-zero positive bounded linear operator on a complex Hilbert space $(H, ⟨ \cdot, \cdot ⟩)$ . Let $ω_{A} (T)$ denote the $A$ -numerical radius of an oper…

math.FA2021★ 1 cited

Further improvements of generalized numerical radius inequalities for Hilbert space operators

Kais Feki

Several new improvements of the $A$ -numerical radius inequalities for operators acting on a semi-Hilbert space, i.e., a space generated by a positive operator $A$ , are proved. In p…

math.FA2020★ 1 cited

Numerical radius inequalities for products and sums of semi-Hilbertian space operators

Pintu Bhunia, Kais Feki, Kallol Paul

New inequalities for the $A$ -numerical radius of the products and sums of operators acting on a semi-Hilbert space, i.e. a space generated by a positive semidefinite operator $A$ ,…

math.FA2020

On $A$ -parallelism and $A$ -Birkhoff-James orthogonality of operators

Tamara Bottazzi, Cristian Conde, Kais Feki

In this paper, we establish several characterizations of the $A$ -parallelism of bounded linear operators with respect to the seminorm induced by a positive operator $A$ acting on a…

math.FA2020★ 2 cited

Further inequalities for the $A$ -numerical radius of certain $2 \times 2$ operator matrices

Kais Feki, Satyajit Sahoo

Let $A = (A 0 0 A)$ be a $2 \times 2$ diagonal operator matrix whose each diagonal entry is a bounded positive (semidefinite) linear op…

math.FA2020

Some bounds for the $A$ -numerical radius of certain $2 \times 2$ operator matrices

Kais Feki

For a given bounded positive (semidefinite) linear operator $A$ on a complex Hilbert space $(H, ⟨ \cdot ∣ \cdot ⟩)$ , we consider the semi-Hilbertian…

math.FA2020

Inequalities for the $A$ -joint numerical radius of two operators and their applications

Kais Feki

Let $(H, ⟨ \cdot ∣ \cdot ⟩)$ be a complex Hilbert space and $A$ be a positive (semidefinite) bounded linear operator on $H$ . The semi-inne…

math.FA2020★ 1 cited

Improved inequalities related to the $A$ -numerical radius for commutators of operators

Kais Feki

Let $A$ be a positive bounded linear operator on a complex Hilbert space $H$ and $B_{A} (H)$ be the subspace of all operators which admit $A$ -adjoints…

math.FA2020★ 4 cited

Joint numerical radius of spherical Aluthge transforms of tuples of Hilbert space operators

Kais Feki, Takeaki Yamazaki

Let $T = (T_{1}, \dots, T_{d})$ be a $d$ -tuple of operators on a complex Hilbert space $H$ . The spherical Aluthge transform of $T$ is the $d$ -tuple given by $\…

math.FA2020

Some $A$ -numerical radius inequalities for $d \times d$ operator matrices

Kais Feki

Let $A$ be a positive (semidefinite) bounded linear operator acting on a complex Hilbert space $(H, ⟨ \cdot ∣ \cdot ⟩)$ . The semi-inner product ${\l…

math.FA2020★ 1 cited

Some $A$ -spectral radius inequalities for $A$ -bounded Hilbert space operators

Kais Feki

Let $r_{A} (T)$ denote the $A$ -spectral radius of an operator $T$ which is bounded with respect to the seminorm induced by a positive operator $A$ on a complex Hilbert space $\mathcal…

math.FA2020★ 60 cited

$A$ -Numerical radius orthogonality and parallelism of semi-Hilbertian space operators and their applications

Pintu Bhunia, Kais Feki, Kallol Paul

In this paper, we aim to introduce and characterize the concept of numerical radius orthogonality of operators on a complex Hilbert space $H$ which are bounded with respe…

math.FA2020★ 8 cited

Some numerical radius inequalities for semi-Hilbert space operators

Kais Feki

Let $A$ be a positive bounded linear operator acting on a complex Hilbert space $(H, ⟨ \cdot ∣ \cdot ⟩)$ . Let $ω_{A} (T)$ and $∥ T ∥_{A}$ denote the $A…

math.FA2019

Davis-Wielandt shells of semi-Hilbertian space operators and its applications

Kais Feki, Sid Ahmed Ould Ahmed Mahmoud

In this paper we generalize the concept of Davis-Wielandt shell of operators on a Hilbert space when a semi-inner product induced by a positive operator $A$ is considered. Moreover…

math.FA2019

Spectral radius of semi-Hilbertian space operators and its applications

Kais Feki

In this paper, we aim to introduce the notion of the spectral radius of bounded linear operators acting on a complex Hilbert space $H$ , which are bounded with respect to…

Joint q-Numerical Ranges of Operators in Hilbert and Semi-Hilbert Spaces

On approximate A-seminorm and A-numerical radius orthogonality of operators

A note on the generalized maximal numerical range of operators

Generalized A-numerical radius of operators and related inequalities

Further improvements of generalized numerical radius inequalities for Hilbert space operators

Numerical radius inequalities for products and sums of semi-Hilbertian space operators

On A-parallelism and A-Birkhoff-James orthogonality of operators

Further inequalities for the A-numerical radius of certain 2×2 operator matrices

Some bounds for the A-numerical radius of certain 2×2 operator matrices

Inequalities for the A-joint numerical radius of two operators and their applications

Improved inequalities related to the A-numerical radius for commutators of operators

Joint numerical radius of spherical Aluthge transforms of tuples of Hilbert space operators

Some A-numerical radius inequalities for d×d operator matrices

Some A-spectral radius inequalities for A-bounded Hilbert space operators

A-Numerical radius orthogonality and parallelism of semi-Hilbertian space operators and their applications

Some numerical radius inequalities for semi-Hilbert space operators

Davis-Wielandt shells of semi-Hilbertian space operators and its applications

Spectral radius of semi-Hilbertian space operators and its applications

Joint $q$ -Numerical Ranges of Operators in Hilbert and Semi-Hilbert Spaces

On approximate $A$ -seminorm and $A$ -numerical radius orthogonality of operators

Generalized $A$ -numerical radius of operators and related inequalities

On $A$ -parallelism and $A$ -Birkhoff-James orthogonality of operators

Further inequalities for the $A$ -numerical radius of certain $2 \times 2$ operator matrices

Some bounds for the $A$ -numerical radius of certain $2 \times 2$ operator matrices

Inequalities for the $A$ -joint numerical radius of two operators and their applications

Improved inequalities related to the $A$ -numerical radius for commutators of operators

Some $A$ -numerical radius inequalities for $d \times d$ operator matrices

Some $A$ -spectral radius inequalities for $A$ -bounded Hilbert space operators

$A$ -Numerical radius orthogonality and parallelism of semi-Hilbertian space operators and their applications