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R. Álvarez-Nodarse

Publications and source records attributed to R. Álvarez-Nodarse.

8 recordsLinked to original sources
arXiv2026

A note on lower bounds for numerical series

After passage to the representing measure, the three principal theorems of Esstafa and Sfaxi, J. Math. Anal. Appl. 556 (2026), 130199, reduce respectively to Jensen's inequality, one quadratic identity, and a one-point measure. We solve the underlying reciprocal-moment problem sharply, determine all extremisers, and obtain a strictly stronger Hurwitz-zeta bound. We also identify the gap between formal inversion and evaluation at 1, and give explicit counterexamples to further analytic claims.

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arXiv2022

On discrete coherent pairs of measures

In [Castillo \& Mbouna, Indag. Math. {\bf 31} (2020) 223-234], the concept of $π_N$-coherent pairs of order $(m,k)$ with index $M$ is introduced. This definition, implicitly related with the standard derivative operator, automatically leaves out the so-called discrete orthogonal polynomials. The purpose of this note is twofold: first we use the (discrete) Hahn difference operator and rewrite the known results in this framework; second, as an application, we describe exhaustively the (discrete) self-coherent pairs in the situation whether $M=0$, $N\leq2$, and $(m,k)=(1,0)$. This is proved by describing in a unified way the classical orthogonal polynomials with respect to Jackson's operator as special or limiting cases of a four parametric family of $q$-polynomials. This gives a partial answer to a conjecture posed by M. E. H Ismail in his monograph [Classical and quantum orthogonal polynomials in one variable, Cambridge University Press, 2005].

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arXiv2019

On classical orthogonal polynomials related to Hahn's operator

Let ${\bf u}$ be a nonzero linear functional acting on the space of polynomials. Let $\mathbf{D}_{q,ω}$ be a Hahn operator acting on the dual space of polynomials. Suppose that there exist polynomials $ϕ$ and $ψ$, with $\mathrm{deg}\,ϕ\leq2$ and $\mathrm{deg}\,ψ\leq1$, so that the functional equation $$ \mathbf{D}_{q,ω}(ϕ{\bf u})=ψ{\bf u} $$ holds, where the involved operations are defined in a distributional sense. In this note we state necessary and sufficient conditions, involving only the coefficients of $ϕ$ and $ψ$, such that ${\bf u}$ is regular, that is, there exists a sequence of orthogonal polynomials with respect to ${\bf u}$. A key step in the proof relies upon the fact that a distributional Rodrigues-type formula holds without assuming that ${\bf u}$ is regular.

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arXiv2017

Uniform convergence of Fourier-Bessel series on a q-linear grid

We study Fourier-Bessel series on a q-linear grid, defined as expansions in complete q-orthogonal systems constructed with the third Jackson q-Bessel function, and obtain sufficient conditions for uniform convergence. The convergence results are illustrated with specific examples of expansions in q-Fourier-Bessel series.

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arXiv2015

Limit relations between $q$-Krall type orthogonal polynomials

In this paper, we consider a natural extension of several results related to Krall-type polynomials introducing a modification of a $q$-classical linear functional via the addition of one or two mass points. The limit relations between the $q$-Krall type modification of big $q$-Jacobi, little $q$-Jacobi, big $q$-Laguerre, and other families of the $q$-Hahn tableau are established.

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arXiv2010

Factorizacion of the hypergeometric-type difference equation on the uniform lattice

We discuss factorization of the hypergeometric-type difference equations on the uniform lattices and show how one can construct a dynamical algebra, which corresponds to each of these equations. Some examples are exhibited, in particular, we show that several models of discrete harmonic oscillators, previously considered in a number of publications, can be treated in a unified form.

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arXiv2010

Factorization of the hypergeometric-type difference equation on the non-uniform lattices: dynamical algebra

We argue that one can factorize the difference equation of hypergeometric type on the nonuniform lattices in general case. It is shown that in the most cases of q-linear spectrum of the eigenvalues this directly leads to the dynamical symmetry algebra $su_q(1,1)$, whose generators are explicitly constructed in terms of the difference operators, obtained in the process of factorization. Thus all models with the $q$-linear spectrum (some of them, but not all, previously considered in a number of publications) can be treated in a unified form.

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