On zero behavior of higher-order Sobolev-type discrete q-Hermite I orthogonal polynomials

Abstract

In this work, we investigate the sequence of monic q-Hermite I-Sobolev type orthogonal polynomials of higher-order, denoted as $\{\mathbb{H}_{n}(x;q)\}_{n\geq 0}$, which are orthogonal with respect to the following non-standard inner product involving q-differences: \begin{equation*} \langle p,q\rangle_{\lambda }=\int_{-1}^{1}f\left( x\right) g\left(x\right) (qx,-qx;q)_{\infty }d_{q}(x)+\lambda \,(\mathscr{D}_{q}^{j}f)(\alpha)(\mathscr{D}_{q}^{j}g)(\alpha), \end{equation*} where $\alpha \in \mathbb{R}\backslash (-1,1)$, $\lambda $ belongs to the set of positive real numbers, $\mathscr{D}_{q}^{j}$ denotes the $j$-th $q $-discrete analogue of the derivative operator, and $(qx,-qx;q)_{\infty}d_{q}(x)$ denotes the orthogonality weight with its points of increase in a geometric progression. We proceed to obtain the hypergeometric representation of $\mathbb{H}_{n}(x;q)$ and explicit expressions for the corresponding ladder operators. From the latter, we obtain a novel kind of three-term recurrence formula with rational coefficients associated with these polynomial family. Moreover, for certain real values of $\alpha $, we present some results concerning the location of the zeros of $\mathbb{H}_n(x;q)$ and we perform a comprehensive analysis of their asymptotic behavior as the parameter $\lambda$ varies from zero to infinity.