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This is a survey on reproducing kernel Krein spaces and their interplay with operator valued Hermitian kernels. Existence and uniqueness properties are carefully reviewed. The approach we follow in this survey uses a more abstract but very…

Functional Analysis · Mathematics 2025-11-04 Aurelian Gheondea

In this work we address the classical problem of classifying tuples of linear operators and linear functions on a finite dimensional vector space up to base change. Having adopted for the situation considered a construction of framed moduli…

Algebraic Geometry · Mathematics 2012-03-15 Stanislav Fedotov

A new functional calculus, developed recently for a fully non-perturbative treatment of quantum gravity, is used to begin a systematic construction of a quantum theory of geometry. Regulated operators corresponding to areas of 2-surfaces…

General Relativity and Quantum Cosmology · Physics 2010-04-06 Abhay Ashtekar , Jerzy Lewandowski

We prove new theorems about properties of generalized functions defined on Gelfand-Shilov spaces $S^\beta$ with $0\le\beta<1$. For each open cone $U\subset\mathbb R^d$ we define a space $S^\beta(U)$ which is related to $S^\beta(\mathbb…

Functional Analysis · Mathematics 2007-08-07 Michael A. Soloviev

Kernel-based approach to operator approximation for partial differential equations has been shown to be unconditionally stable for linear PDEs and numerically exhibit unconditional stability for non-linear PDEs. These methods have the same…

Numerical Analysis · Mathematics 2025-11-25 Andrew Christlieb , Sining Gong , Hyoseon Yang

A unified approach is given to kernel functions which intertwine Ruijsenaars difference operators of type A and of type BC. As an application of the trigonometric cases, new explicit formulas for Koornwinder polynomials attached to single…

Quantum Algebra · Mathematics 2009-05-17 Yasushi Komori , Masatoshi Noumi , Jun'ichi Shiraishi

This paper investigates the composition of Bernstein--Durrmeyer operators and Sz\'asz--Mirakjan--Durrmeyer operators, focusing on the structure and properties of the associated kernel functions. In the case of the Bernstein--Durrmeyer…

Classical Analysis and ODEs · Mathematics 2025-07-01 Ulrich Abel , Ana Maria Acu , Margareta Heilmann , Ioan Raşa

A representation for the kernel of the transmutation operator relating the perturbed Bessel equation with the unperturbed one is obtained in the form of a functional series with coefficients calculated by a recurrent integration procedure.…

Classical Analysis and ODEs · Mathematics 2017-12-06 Vladislav V. Kravchenko , Elina L. Shishkina , Sergii M. Torba

This note characterizes multiplicative linear functionals on reproducing kernel Hilbert spaces of functions on the Euclidean unit ball in complex d-dimensional space, in terms of their action on kernel functions. The kernels considered are…

Functional Analysis · Mathematics 2026-05-22 Tirthankar Bhattacharyya , Jaikishan , Poornendu Kumar

This paper reviews the functional aspects of statistical learning theory. The main point under consideration is the nature of the hypothesis set when no prior information is available but data. Within this framework we first discuss about…

Machine Learning · Statistics 2016-11-25 Stephane Canu , Xavier Mary , Alain Rakotomamonjy

We introduce an operator valued Short-Time Fourier Transform for certain classes of operators with operator windows, and show that the transform acts in an analogous way to the Short-Time Fourier Transform for functions, in particular…

Functional Analysis · Mathematics 2023-06-08 Monika Dörfler , Franz Luef , Henry McNulty , Eirik Skrettingland

Coherent, continuous spatial representations are critical for synthesizing physical and perceptual phenomena into a single representational space. Radial basis kernels provide a path forward for this type of distributed representation. In…

Machine Learning · Computer Science 2026-05-12 Jakeb Chouinard

This is a tutorial and survey paper on kernels, kernel methods, and related fields. We start with reviewing the history of kernels in functional analysis and machine learning. Then, Mercer kernel, Hilbert and Banach spaces, Reproducing…

Machine Learning · Statistics 2021-06-17 Benyamin Ghojogh , Ali Ghodsi , Fakhri Karray , Mark Crowley

We consider a class of maps from integral Hankel operators to Hankel matrices, which we call restriction maps. In the simplest case, such a map is simply a restriction of the integral kernel onto integers. More generally, it is given by an…

Functional Analysis · Mathematics 2018-10-02 Nazar Miheisi , Alexander Pushnitski

In this paper, we explore the relationship between the operators mapping atoms to molecules in local Hardy spaces $h^p(\mathbb{R}^n)$ and the size conditions of its kernel. In particular, we show that if the kernel of a…

Classical Analysis and ODEs · Mathematics 2025-08-13 Chun Ho Lau , Claudio Vasconcelos

In this paper, by using the decomposition theorem for weak Hardy spaces, we will obtain the boundedness properties of some integral operators with variable kernels on these spaces, under some Dini type conditions imposed on the variable…

Classical Analysis and ODEs · Mathematics 2014-01-27 Hua Wang

We continue the construction of the $:\phi^4_4:$ quantum field theory. In this paper we consider the Wick kernel of the interacting quantum field. Using the complex structure and the Fock-Bargmann-Berezin-Segal integral representation we…

High Energy Physics - Theory · Physics 2008-02-03 Edward P. Osipov

Targeting at sparse learning, we construct Banach spaces B of functions on an input space X with the properties that (1) B possesses an l1 norm in the sense that it is isometrically isomorphic to the Banach space of integrable functions on…

Machine Learning · Statistics 2015-01-16 Guohui Song , Haizhang Zhang , Fred J. Hickernell

In a digraph, a kernel is a subset of vertices that is both independent and absorbing. Kernels have important applications in combinatorics and outside. Kernels do not always exist and finding sufficient conditions ensuring their existence…

Combinatorics · Mathematics 2025-02-05 Hélène Langlois , Frédéric Meunier

Motivated by the study of H\"ormander's sums-of-squares operators and their generalizations, we define the convolution algebra of transverse distributions associated to a singular foliation. We prove that this algebra is represented as…

Analysis of PDEs · Mathematics 2020-04-20 Iakovos Androulidakis , Omar Mohsen , Robert Yuncken