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In this paper we introduce the concept of quadratic operator perspective for a continuous function {\Phi} defined on the positive semi-axis of real numbers. This generalize the quadratic weighted operator geometric mean and the quadratic…

Functional Analysis · Mathematics 2016-09-29 Silvestru Sever Dragomir

Recent innovations in the differential calculus for functions of non-commuting variables, beginning with a quaternionic variable, are now extended to consider some integration.

Functional Analysis · Mathematics 2008-08-18 Charles Schwartz

Notions of a "holomorphic" function theory for functions of a split-quaternionic variable have been of recent interest. We describe two found in the literature and show that one notion encompasses a small class of functions, while the other…

Complex Variables · Mathematics 2015-06-25 John A. Emanuello , Craig A. Nolder

In this paper, we study joint functional calculus for commuting $n$-tuple of Ritt operators. We provide an equivalent characterisation of boundedness for joint functional calculus for Ritt operators on $L^p$-spaces, $1< p<\infty$. We also…

Classical Analysis and ODEs · Mathematics 2020-12-14 Parasar Mohanty , Samya Kumar Ray

There are presented certain results on extending continuous linear operators defined on spaces of E-valued continuous functions (defined on a compact Hausdorff space X) to linear operators defined on spaces of E-valued measurable functions…

Functional Analysis · Mathematics 2017-05-26 Piotr Niemiec

we start the study of Schur analysis in the quaternionic setting using the theory of slice hyperholomorphic functions. The novelty of our approach is that slice hyperholomorphic functions allows to write realizations in terms of a suitable…

Functional Analysis · Mathematics 2011-10-13 Daniel Alpay , Fabrizio Colombo , Irene Sabadini

Harmonic and polyanalytic functional calculi have been recently defined for bounded commuting operators. Their definitions are based on the Cauchy formula of slice hyperholomorphic functions and on the factorization of the Laplace operator…

Spectral Theory · Mathematics 2023-04-21 Fabrizio Colombo , Antonino De Martino , Stefano Pinton

In this paper, we introduce and study frame of operators in quaternionic Hilbert spaces as a generalization of g frames which in turn generalized various notions like Pseduo frames, bounded quasi-projectors and frame of subspaces (fusion…

Functional Analysis · Mathematics 2020-03-03 S. K. Sharma , A. M. Jarrah , S. K. Kaushik

In this paper a new variational approach concerning functions (continuous) over Hilbert spaces is presented.

Functional Analysis · Mathematics 2016-08-23 Antoine Mhanna

The $S$-functional calculus for slice hyperholomorphic functions generalizes the Riesz-Dunford-functional calculus for holomorphic functions to quaternionic linear operators and to $n$-tuples of noncommuting operators. For an unbounded…

Spectral Theory · Mathematics 2016-02-15 Jonathan Gantner

We define the concept of completely regular ordinary differential operators and give various criteria for operators to belong to this class. We give also criteria for Birkhof regularity of ordinary differential operators in terms of the…

Spectral Theory · Mathematics 2007-07-06 E. A. Shiryaev , A. A. Shkalikov

In this note first we study the Weyl operators and Weyl S-spectrum of a bounded right quaternionic linear operator, in the setting of the so-called S-spectrum, in a right quaternionic Hilbert space. In particular, we give a characterization…

Mathematical Physics · Physics 2018-10-12 B. Muraleetharan , K. Thirulogasanthar

We study properties of inner and outer functions in the Hardy space of the quaternionic unit ball. In particular, we give sufficient conditions as well as necessary ones for functions to be inner or outer.

Complex Variables · Mathematics 2019-03-06 Alessandro Monguzzi , Giulia Sarfatti , Daniel Seco

Functional analysis, especially the theory of Hilbert spaces and of operators on these, form an important area in mathematics. We formalized the Isabelle/HOL library Complex_Bounded_Operators containing a large amount of theorems about…

Logic in Computer Science · Computer Science 2025-12-08 Dominique Unruh , José Manuel Rodríguez Caballero

This dissertation focuses on developing a new construction of a functional calculus using Henstock-Kurzweil integration methods. The assignment of a functional calculus will be applied to self-adjoint operators. We will address both the…

Functional Analysis · Mathematics 2025-11-18 Marin Matei-Luca

Based on a new generalization of Cauchy-Riemann system presented in this paper, we introduce a class of quaternion-valued functions of a quaternionic variable, which are called algebraic regular functions. The set of algebraic regular…

Complex Variables · Mathematics 2015-11-30 Keqin Liu

In [1], an operator was introduced which acts parallel to the Riemann-Liouville differintegral on a transformation of the space of real analytic functions and commutes with itself. This paper aims to extend the technique - and its defining…

Classical Analysis and ODEs · Mathematics 2012-07-31 Matthew Parker

Spectral theory and functional calculus for unbounded self-adjoint operators on a Hilbert space are usually treated through von Neumann's Cayley transform. Based on ideas of Woronowicz, we redevelop this theory from the point of view of…

Operator Algebras · Mathematics 2016-09-14 Christian Budde , Klaas Landsman

The $H^\infty$-functional calculus is a two-step procedure, introduced by A. McIntosh, that allows the definition of functions of sectorial operators in Banach spaces. It plays a crucial role in the spectral theory of differential…

Spectral Theory · Mathematics 2025-06-23 Fabrizio Colombo , Francesco Mantovani , Peter Schlosser

General, especially spectral, features of compact normal operators in quaternionic Hilbert spaces are studied and some results are established which generalize well-known properties of compact normal operators in complex Hilbert spaces.…

Functional Analysis · Mathematics 2014-02-14 Riccardo Ghiloni , Valter Moretti , Alessandro Perotti