Orthogonal Constant Mappings in Isosceles Orthogonal Spaces

Szegő映射与Hermite–Padé多项式用于单位圆上的多重正交性

Szegő Mapping and Hermite--Padé Polynomials for Multiple Orthogonality on the Unit Circle

本文研究了单位圆上满足多重正交条件的多项式，通过Szegő映射和Geronimus关系将其与实线上多重正交多项式联系起来，推导了多项种递推关系和行列式表示。

A Fixed Point Approach to Stability of a Quadratic Equation

Using the fixed point alternative theorem we establish the orthogonal stability of quadratic functional equation of Pexider type $f(x+y)+g(x-y)=h(x)+k(y)$, where $f, g, h, k$ are mappings from a symmetric orthogonality space to a Banach space, by orthogonal additive mappings under a necessary and sufficient condition on $f$.

$H_q-$semiclassical orthogonal polynomials via polynomial mappings

In this work we study orthogonal polynomials via polynomial mappings in the framework of the $H_q-$semiclassical class. We consider two monic orthogonal polynomial sequences $\{p_n (x)\}_{n\geq0}$ and $\{q_n(x)\}_{n\geq0}$ such that $$ p_{kn}(x)=q_n(x^k)\;,\quad n=0,1,2,\ldots\;, $$ being $k$ a fixed integer number such that $k\geq2$, and we prove that if one of the sequences $\{p_n (x)\}_{n\geq0}$ or $\{q_n(x)\}_{n\geq0}$ is $H_q-$semiclassical, then so is the other one. In particular, we show that if $\{p_n(x)\}_{n\geq0}$ is $H_q-$semiclassical of class $s\leq k-1$, then $\{q_n (x)\}_{n\geq0…

Spacing properties of the zeros of orthogonal polynomials on Cantor sets via a sequence of polynomial mappings

Let $μ$ be a probability measure with an infinite compact support on $\mathbb{R}$. Let us further assume that $(F_n)_{n=1}^\infty$ is a sequence of orthogonal polynomials for $μ$ where $(f_n)_{n=1}^\infty$ is a sequence of nonlinear polynomials and $F_n:=f_n\circ\dots\circ f_1$ for all $n\in\mathbb{N}$. We prove that if there is an $s_0\in\mathbb{N}$ such that $0$ is a root of $f_n^\prime$ for each $n>s_0$ then the distance between any two zeros of an orthogonal polynomial for $μ$ of a given degree greater than $1$ has a lower bound in terms of the distance between the set of critical points a…

Function theory of antilinear operators

Unlike in complex linear operator theory, polynomials or, more generally, Laurent series in antilinear operators cannot be modelled with complex analysis. There exists a corresponding function space, though, surfacing in spectral mapping theorems. These spectral mapping theorems are inclusive in general. Equality can be established in the self-adjoint case. The arising functions are shown to possess a biradial character. It is shown that to any given set of Jacobi parameters corresponds a biradial measure yielding these parameters in an iterative orthogonalization process in this function spac…

The reproducing kernel structure arising from a combination of continuous and discrete orthogonal polynomials into Fourier systems

We study mapping properties of operators with kernels defined via a combination of continuous and discrete orthogonal polynomials, which provide an abstract formulation of quantum (q-) Fourier type systems. We prove Ismail conjecture regarding the existence of a reproducing kernel structure behind these kernels, by establishing a link with Saitoh theory of linear transformations in Hilbert space. The results are illustrated with Fourier kernels with ultraspherical weights, their continuous q-extensions and generalizations. As a byproduct of this approach, a new class of sampling theorems is ob…