M. Abtahi

activity

20122025

most citedFixed point theorems for Meir-Keeler type contractions in metric spaces

8 citations · 24 across the 13 of their papers we have counts for

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10 papers · 1 filter

math.FA2025

A characterization of compact operators on $ℓ^{p}$ -spaces

Mortaza Abtahi

Let $A$ be a Banach space, $p > 1$ , and $1/ p + 1/ q = 1$ . If a sequence $a = (a_{i})$ in $A$ has a finite $p$ -sum, then the operator $Λ_{a} : ℓ^{q} \to A$ , defined by $Λ_a(β)=\sum_{i=1}^\infty β_…

math.FA2023

Algebras of Polynomials Generated by Linear Operators

F. Zaj, M. Abtahi

Let $E$ be a Banach space and $A$ be a commutative Banach algebra with identity. Let $P (E, A)$ be the space of $A$ -valued polynomials on $E$ generated by bounded linear operators…

math.FA2023

Regularity conditions for vector-valued function algebras

Z. Barqi, M. Abtahi

We consider several notions of regularity, including strong regularity, bounded relative units, and Ditkin's condition, in the setting of vector-valued function algebras. Given a c…

math.FA2022★ 5 cited

An extension of Birkhoff--James orthogonality relations in semi-Hilbertian space operators

S. M. Enderami, M. Abtahi, A. Zamani

Let $B (H)$ denote the $C^{*}$ -algebra of all bounded linear operators on a Hilbert space $(H, ⟨ \cdot, \cdot ⟩)$ . Given a positive…

math.FA2022

An orthogonality relation in complex normed spaces based on norm derivatives

S. M. Enderami, M. Abtahi, A. Zamani +1

Let $X$ be a complex normed space. Based on the right norm derivative $ρ_{_{+}}$ , we define a mapping $ρ_{_{\infty}}$ by \begin{equation*} ρ_{_{\infty}}(x,y) = \frac1π\int_0^{2π}e^…

math.FA2017

A Characterization of Polynomially Convex Sets in Banach Spaces

Mortaza Abtahi, Sara Farhangi

Let $E$ be a Banach space and $\X$ be the closed unit ball of the dual space $E^{*}$ . For a compact set $K$ in $E$ , we prove that $K$ is polynomially convex in $E$ if and only if the…

math.FA2016

On the character space of Banach vector-valued function algebras

Mortaza Abtahi

Given a compact space $X$ and a commutative Banach algebra $A$ , the character spaces of $A$ -valued function algebras on $X$ are investigated. The class of natural $A$ -valued functi…

math.FA2015

Vector-valued spectra of Banach algebra valued continuous functions

Mortaza Abtahi, Sara Farhangi

Given a compact space $X$ , a commutative Banach algebra $A$ , and an $A$ -valued function algebra $A$ on $X$ , the notions of vector-valued spectrum of functions $f\in\maths…

math.FA2015★ 8 cited

Vector-valued characters on Vector-valued Function Algebras

Mortaza Abtahi

Let $A$ be a commutative Banach algebra and $X$ be a compact space. The class of Banach $A$ -valued function algebras on $X$ consists of subalgebras of $C (X, A)$ with certain propert…

math.FA2012

New characterizations of maximal ideals in algebras of continuous vector-valued functions

Mortaza Abtahi

Let X be a compact Hausdorf space, let A be a commutative unital Banach algebra, and let C(X,A) denote the algebra of continuous A-valued functions on $X$ equipped with the uniform…

A characterization of compact operators on ℓp-spaces

Algebras of Polynomials Generated by Linear Operators

Regularity conditions for vector-valued function algebras

An extension of Birkhoff--James orthogonality relations in semi-Hilbertian space operators

An orthogonality relation in complex normed spaces based on norm derivatives

A Characterization of Polynomially Convex Sets in Banach Spaces

On the character space of Banach vector-valued function algebras

Vector-valued spectra of Banach algebra valued continuous functions

Vector-valued characters on Vector-valued Function Algebras

New characterizations of maximal ideals in algebras of continuous vector-valued functions

A characterization of compact operators on $ℓ^{p}$ -spaces