Asymptotic behaviour of some families of orthonormal polynomials and an associated Hilbert space

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• 作者：Aleksandar Ignjatović ^{ignjat@cse.unsw.edu.au" class="auth_mail" title="E-mail the corresponding author}
• 关键词：42C05 ; 41A60 ; 42A75
• 刊名：Journal of Approximation Theory
• 出版年：2016
• 出版时间：October 2016
• 年：2016
• 卷：210
• 期：Complete
• 页码：41-79
• 全文大小：522 K

文摘

We characterise asymptotic behaviour of families of symmetric orthonormal polynomials whose recursion coefficients satisfy certain conditions, satisfied for example by the (normalised) Hermite polynomials. More generally, these conditions are satisfied by the recursion coefficients of the form c(n+1)^p$c{(n+1)}^p$ for 0<p<1$0<p<1$ and c>0$c>0$, as well as by recursion coefficients which correspond to polynomials orthonormal with respect to the exponential weight W(x)=exp(−|x|^β)$W\left(x\right)=exp(-{\left|x\right|}^{\beta })$ for β>1$\beta >1$. We use these results to show that, in a Hilbert space defined in a natural way by such a family of orthonormal polynomials, every two complex exponentials $e_{\omega }\left(t\right)=e^{\dot{ı}\omega t}$ and $e_{\sigma }\left(t\right)=e^{\dot{ı}\sigma t}$ of distinct frequencies ω,σ$\omega ,\sigma$ are mutually orthogonal. We finally formulate a surprising conjecture for the corresponding families of non-symmetric orthonormal polynomials; extensive numerical tests indicate that such a conjecture appears to be true.