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Given any square matrix or a bounded operator $A$ in a Hilbert space such that $p(A)$ is normal (or similar to normal), we construct a Banach algebra, depending on the polynomial $p$, for which a simple functional calculus holds. When the…

Functional Analysis · Mathematics 2015-06-03 Olavi Nevanlinna

Let ${\mathbb{D}}=\{z\in \mathbb{C}:|z|<1\}$ and for an integer $d\geq 1$, let $S_d$ denote the symmetric group, consisting of of all permutations of the set $\{1,\cdots, d\}$. A function $f:{\mathbb{D}}^d\rightarrow \mathbb{C}$ is…

Functional Analysis · Mathematics 2022-01-07 Amol Sasane

We introduce the concept of an $E$-valued function algebra, a type of Banach algebra that consist of continuous $E$-valued functions on some compact Hausdorff space, where $E$ is a Banach algebra. We present some basic results about such…

Functional Analysis · Mathematics 2020-08-12 Azadeh Nikou , Anthony G. O'Farrell

We propose the Lie-algebraic interpretation of poly-analytic functions in $L_2(\C,d\mu)$, with the Gaussian measure $d\mu$, based on a flag structure formed by the representation spaces of the $\mathfrak{sl}(2)$-algebra realized by…

Complex Variables · Mathematics 2021-10-14 Alexander V Turbiner , Nikolai L Vasilevski

In Mergelyan type approximation we uniformly approximate functions on compact sets K by polynomials or rational functions or holomorphic functions on varying open sets containing K. In the present paper we consider analogous approximation,…

Complex Variables · Mathematics 2020-06-04 Sotiris Armeniakos , Giorgos Kotsovolis , Vassili Nestoridis

Let $X$ be a real separable normed space $X$ admitting a separating polynomial. We prove that each continuous function from a subset $A$ of $X$ to a real Banach space can be uniformly approximated by restrictions to $A$ of functions which…

Functional Analysis · Mathematics 2020-04-03 M. A. Mytrofanov , A. V. Ravsky

Let C(K) denote the Banach algebra of continuous real functions, with the supremum norm, on a compact Hausdorff space K. For two subsets of C(K), one can define their product by pointwise multiplication, just as the Minkowski sum of the…

Functional Analysis · Mathematics 2016-04-06 Jose Pedro Moreno , Rolf Schneider

Let $D$ be the open unit disc in the complex plane. We denote by $\mathbb{C}$ the set of complex numbers and consider any compact set $K$ which is disjoint from $D$ and which also has connected complement. Let $A(K)$ denote all the…

Complex Variables · Mathematics 2015-06-05 Nikos Tsirivas

In this note we study the endomorphisms of certain Banach algebras of infinitely differentiable functions on compact plane sets, associated with weight sequences M. These algebras were originally studied by Dales, Davie and McClure. In a…

Functional Analysis · Mathematics 2007-05-23 J. F. Feinstein , Herbert Kamowitz

In this short note, we first consider some inequalities for comparison of some algebraic properties of two continuous algebra-multiplications on an arbitrary Banach space and then, as an application, we consider some very basic observations…

Functional Analysis · Mathematics 2019-07-24 Maysam Maysami Sadr

We introduce a new functional space U designed to contain all classical arithmetic functions (Mobius, von Mangoldt, Euler phi, divisor functions, Dirichlet characters, etc.). The norm of U combines a Hilbert-type component, based on square…

General Mathematics · Mathematics 2025-10-02 Es-said En-naoui

We study Banach $\widetilde{\mathbb C}$-algebras, i.e., complete ultra-pseudo-normed algebras over the ring $\widetilde{\mathbb C}$ of Colombeau generalized complex numbers. We develop a spectral theory in such algebras. We show by explicit…

Functional Analysis · Mathematics 2008-11-12 Hans Vernaeve

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 there exist a unital commutative Banach algebra $A$ and a…

Functional Analysis · Mathematics 2017-05-19 Mortaza Abtahi , Sara Farhangi

In this article, we propose a $p$-adic analogue of complex Hilbert space and consider generalizations of some well-known theorems from functional analysis and the basic study of operators on Hilbert spaces. We compute the $K$-theory of the…

Operator Algebras · Mathematics 2019-07-17 Anton Claußnitzer , Andreas Thom

The main goal of this work is to introduce an analogous in the non-archimedean context of the Gelfand spaces of certain Banach commutative algebras with unit. In order to do that, we study the spectrum of this algebras and we show that,…

Functional Analysis · Mathematics 2015-06-17 Jose Aguayo , Miguel Nova , Jacqueline Ojeda

We describe the multiplier algebra of the noncommutative Schwartz space. This multiplier algebra can be seen as the largest ${}^*$-algebra of unbounded operators on a separable Hilbert space with the classical Schwartz space of rapidly…

Functional Analysis · Mathematics 2021-03-10 Tomasz Ciaś , Krzysztof Piszczek

Suppose that $B$ is a $G$-Banach algebra over $\mathbb{F} = \mathbb{R}$ or $\mathbb{C}$, $X$ is a finite dimensional compact metric space, $\zeta : P \to X$ is a standard principal $G$-bundle, and $A_\zeta = \Gamma (X, P \times_G B)$ is the…

Operator Algebras · Mathematics 2012-01-12 Emmanuel Dror Farjoun , Claude L. Schochet

We use weighted polynomial approximation to prove the existence of a compact set K with non-empty interior and a function f is dense in the space A(K) of all continuous functions on K that are holomorphic in the interior of K, endowed with…

Complex Variables · Mathematics 2025-06-26 Stéphane Charpentier , Konstantinos Maronikolakis

This paper presents a solution to a problem from superanalysis about the existence of Hilbert-Banach superalgebras. Two main results are derived: 1) There exist Hilbert norms on some graded algebras (infinite-dimensional superalgebras…

funct-an · Mathematics 2007-05-23 Joachim Kupsch , Oleg G. Smolyanov

On the one hand the algebras of linear operators here act on finite-dimensional vector spaces, and on the other hand the point of view is generally an analysts'. Also, one might think of algebras as being used to add more data to basic…

Classical Analysis and ODEs · Mathematics 2007-05-23 Stephen Semmes