Kerstin Jordaan, Maurice Kenfack Nangho
We study a limiting case of the Askey-Wilson polynomials when one of the parameters goes to infinity, namely continuous dual q-Hahn polynomials when q > 1. Solutions to the associated indeterminate moment problem by general theory are found and an orthogonality relation is established.
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For a class of orthogonal polynomials related to the $q$-Meixner polynomials corresponding to an indeterminate moment problem we give a one-parameter family of orthogonality measures. For these measures we complement the orthogonal polynomials to an orthogonal basis for the corresponding weighted $L^2$-space explicitly. The result is proved in two ways; by a spectral decomposition of a suitable operator and by direct series manipulation. We discuss extensions to explicit non-positive measures and the relation to other indeterminate moment problems for the continuous $q^{-1}$-Hahn and $q$-Lague…
We study the Plancherel--Rotach asymptotics of four families of orthogonal polynomials, the Chen--Ismail polynomials, the Berg-Letessier-Valent polynomials, the Conrad--Flajolet polynomials I and II. All these polynomials arise in indeterminate moment problems and three of them are birth and death process polynomials with cubic or quartic rates. We employ a difference equation asymptotic technique due to Z. Wang and R. Wong. Our analysis leads to a conjecture about large degree behavior of polynomials orthogonal with respect to solutions of indeterminate moment problems.
Laurent polynomials related to the Hahn-Exton $q$-Bessel function, which are $q$-analogues of the Lommel polynomials, have been introduced by Koelink and Swarttouw. The explicit strong moment functional with respect to which the Laurent $q$-Lommel polynomials are orthogonal is given. The strong moment functional gives rise to two positive definite moment functionals. For the corresponding sets of orthogonal polynomials the orthogonality measure is determined using the three-term recurrence relation as a starting point. The relation between Chebyshev polynomials of the second kind and the Laure…
In this paper we characterise the indeterminate case by the eigenvalues of the Hankel matrices being bounded below by a strictly positive constant. An explicit lower bound is given in terms of the orthonormal polynomials and we find expresions for this lower bound in a number of indeterminate moment problems.
Indeterminate Stieltjes moment problems revisited
本文重新审视并证明了关于Stieltjes意义下动量问题确定性和不定性的新结果。
The generalized Stieltjes--Wigert polynomials depending on parameters 0\le p<1 and 0<q<1 are discussed. By removing the mass at zero of the N-extremal solution concentrated in the zeros of the D-function from the Nevanlinna parametrization, we obtain a discrete measure μ^M which is uniquely determined by its moments. We calculate the coefficients of the corresponding orthonormal polynomials (P^M_n). As noticed by Chihara, these polynomials are the shell polynomials corresponding to the maximal parameter sequence for a certain chain sequence. We also find the minimal parameter sequence, as well…
An upper bound for the Nevanlinna matrix of an indeterminate moment sequence
本研究针对不定Hamburger矩问题，通过将其转化为极限圆情形的典范系统，给出了Nevanlinna矩阵增长的显式可计算上界，且该界对性态良好的参数是紧的。
On the entropy for indeterminate moment problems
本文研究了不定矩问题中解析密度的熵性质，证明了无限族密度具有有限熵，并通过Al-Salam--Carlitz问题示例说明。
For an indeterminate moment problem we denote the orthonormal polynomials by P_n. We study the relation between the growth of the function P(z)=(\sum_{n=0}^\infty|P_n(z)|^2)^{1/2} and summability properties of the sequence (P_n(z)). Under certain assumptions on the recurrence coefficients from the three term recurrence relation zP_n(z)=b_nP_{n+1}(z)+a_nP_n(z)+b_{n-1}P_{n-1}(z), we show that the function P is of order αwith 0<α<1, if and only if the sequence (P_n(z)) is absolutely summable to any power greater than 2α. Furthermore, the order αis equal to the exponent of convergence of the seque…
Let $(s_n)_{n\ge 0}$ denote an indeterminate Hamburger moment sequence and let $\mathcal H=\{s_{m+n}\}$ be the corresponding positive definite Hankel matrix. We consider the question if there exists an infinite symmetric matrix $\mathcal A=\{a_{j,k}\}$, which is an inverse of $\mathcal H$ in the sense that the matrix product $\mathcal A\mathcal H$ is defined by absolutely convergent series and $\mathcal A\mathcal H$ equals the identity matrix $\mathcal I$, a property called (aci). A candidate for $\mathcal A$ is the coefficient matrix of the reproducing kernel of the moment problem, considered…
Full indefinite Stieltjes moment problem is studied via the step-by-step Schur algorithm. Naturally associated with indefinite Stieltjes moment problem are generalized Stieltjes continued fraction and a system of difference equations, which, in turn, lead to factorization of resolvent matrices of indefinite Stieltjes moment problem. A criterion for such a problem to be indeterminate in terms of continued fraction is found and a complete description of its solutions is given in the indeterminate case. Explicit formulae for diagonal and sub-diagonal Padé approximants for formal power series corr…
We study the $q$-hypergeometric difference operator $L$ on a particular Hilbert space. In this setting $L$ can be considered as an extension of the Jacobi operator for $q^{-1}$-Al-Salam--Chihara polynomials. Spectral analysis leads to unitarity and an explicit inverse of a $q$-analog of the Jacobi function transform. As a consequence a solution of the Al-Salam--Chihara indeterminate moment problem is obtained.
Starting from the moment sequences of classical orthogonal polynomials we derive the orthogonality purely algebraically. We consider also the moments of ($q=1$) classical orthogonal polynomials, and study those cases in which the exponential generating function has a nice form. In the opposite direction, we show that the generalized Dumont-Foata polynomials with six parameters are the moments of rescaled continuous dual Hahn polynomials. Finally we show that one of our methods can be applied to deal with the moments of Askey-Wilson polynomials.
In 1998 G. Valent made conjectures about the order and type of certain indeterminate Stieltjes moment problems associated with birth and death processes having polynomial birth and death rates of degree p\ge 3. Romanov recently proved that the order is 1/p as conjectured, see \cite{Ro}. We prove that the type with respect to the order is related to certain multi-zeta values and that this type belongs to the interval [π/(p\sin(π/p)),π/(p\sin(π/p)\cos(π/p))], which also contains the conjectured value. This proves that the conjecture about type is asymptotically correct as p\to\infty. The main id…
In 1993 Delest and Fédou showed that a generating function for connected skew shapes is given as a ratio $J_{ν+1}/J_ν$ of the Hahn--Exton $q$-Bessel functions when a parameter $ν$ is zero. They conjectured that when $ν$ is a nonnegative integer the coefficients of the generating function are rational functions whose numerator and denominator are polynomials in $q$ with nonnegative integer coefficients, which is a $q$-analog of Kishore's 1963 result on Bessel functions. The first main result of this paper is a proof of the conjecture of Delest and Fédou. The second main result is a refinement o…
We investigate the quadratic decomposition and duality to classify symmetrical $H_{q}$-semiclassical orthogonal $q$-polynomials of class one where $H_{q}$ is the Hahn's operator. For any canonical situation, the recurrence coefficients, the $q$-analog of the distributional equation of Pearson type, the moments and integral or discrete representations are given.
We study two families of orthogonal polynomials. The first is a finite family related to the Askey-Wilson polynomials but the orthogonality is on the real line. A limiting case of this family is an infinite system of orthogonal polynomials whose moment problem is indeterminate. We provide several orthogonality measures for the infinite family and derive their Plancherel-Rotach asymptotics.
The Hamburger Criterion for Matrix Nevanlinna--Pick Interpolation
本文针对矩阵Nevanlinna–Pick插值问题，建立了类似经典汉堡矩问题不确定性准则的新准则，该准则基于相关矩阵级数的收敛性表述。
The symmetric Al-Salam--Chihara polynomials for $q>1$ are associated with an indeterminate moment problem. There is a self-adjoint second order difference operator on $\ell^2(\Z)$ to which these polynomials are eigenfunctions. We determine the spectral decomposition of this self-adjoint operator. This leads to a class of discrete orthogonality measures, which have been obtained previously by Christiansen and Ismail using a different method, and we give an explicit orthogonal basis for the corresponding weighted $\ell^2$-space. In particular, the orthocomplement of the polynomials is described …
Asymptotics, orthogonality relations and duality for the $q$ and $q^{-1}$-symmetric polynomials in the $q$-Askey scheme
本文综述了q-Askey方案中q与q^{-1}-对称多项式及其对偶族的已知正交关系，利用对称极限导出连续大q^{-1}-Hermite多项式的新无穷离散正交关系，并通过Darboux方法给出大阶数渐近性。
The Stieltjes-Wigert polynomials, which correspond to an indeterminate moment problem on the positive half-line, are eigenfunctions of a second order q-difference operator. We consider the orthogonality measures for which the difference operator is symmetric in the corresponding weighted $L^2$-spaces. These measures are exactly the solutions to the q-Pearson equation.In the case of discrete and absolutely continuous measures the difference operator is essentially self-adjoint, and the corresponding spectral decomposition is given explicitly. In particular, we find an orthogonal set of q-Bessel…
We show that a confluent case of the big q-Jacobi polynomials P_n(x;a,b,c;q), which corresponds to a=b=-c, leads to a discrete orthogonality relation for imaginary values of the parameter a (outside of its commonly known domain 0<a< q^{-1}). Since P_n(x;q^α, q^α, -q^α; q) tend to Gegenbauer (or ultraspherical) polynomials in the limit as q->1, this family represents yet another q-extension of these classical polynomials, different from the continuous q-ultraspherical polynomials of Rogers. The dual family with respect to the polynomials P_n(x;a,a,-a;q) (i.e., the dual discrete q-ultraspherical…
We consider the Stieltjes moment problem for the Berg-Urbanik semigroups which form a class of multiplicative convolution semigroups on $\mathbb{R}_+$ that is in bijection with the set of Bernstein functions. Berg and Durán proved that the law of such semigroups is moment determinate (at least) up to time $t=2$, and, for the Bernstein function $ϕ(u)=u$, Berg made the striking observation that for time $t>2$ the law of this semigroup is moment indeterminate. We extend these works by estimating the threshold time $\scr{T}_ϕ\in [2,\infty]$ that it takes for the law of such Berg-Urbanik semigroups…
The dual discrete $q$-ultraspherical polynomials $D_n^{(s)}(μ(x;s)|q)$ correspond to indeterminate moment problem and, therefore, have one-parameter family of extremal orthogonality relations. It is shown that special cases of dual discrete $q$-ultraspherical polynomials $D_n^{(s)}(μ(x;s)|q)$, when $s=q^{-1}$ and $s=q$, are directly connected with $q^{-1}$-Hermite polynomials. These connections are given in an explicit form. Using these relations, all extremal orthogonality relations for these special cases of polynomials $D_n^{(s)}(μ(x;s)|q)$ are found.
Growth estimates for Nevanlinna matrices of order larger than one half
针对不确定 Hamburger 矩问题与极限圆 Jacobi 算子导出的二维正则系统，本文建立了大阶（>1/2）情形下单值矩阵增长的显式新下界，并计算了临界情形下 Nevanlinna 矩阵的阶。
Bidiagonal Factorization of Banded Recursion Matrices for Mixed-Type Multiple Orthogonal Polynomials
本文通过Christoffel变换构造带状矩阵的双对角分解，用于研究振荡带状矩阵和多正交多项式的谱Favard定理。
Bessel Multiple Orthogonal Polynomials of Mixed Type
本文针对单位圆上的$q\times p$矩阵权构造混合型类贝塞尔多重正交多项式，推导其公式、正交性、表示式与递推关系，明确$q=1$时的分解特性。
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