Spectral analysis of non-self-adjoint Jacobi operator associated with Jacobian elliptic functions

We perform the spectral analysis of a family of Jacobi operators $J(\alpha)$ depending on a complex parameter $\alpha$. If $|\alpha|\neq1$ the spectrum of $J(\alpha)$ is discrete and formulas for eigenvalues and eigenvectors are established in terms of elliptic integrals and Jacobian elliptic functions. If $|\alpha|=1$, $\alpha \neq \pm 1$, the essential spectrum of $J(\alpha)$ covers the entire complex plane. In addition, a formula for the Weyl $m$-function as well as the asymptotic expansions of solutions of the difference equation corresponding to $J(\alpha)$ are obtained. Finally, the completeness of eigenvectors and Rodriguez-like formulas for orthogonal polynomials, studied previously by Carlitz, are proved.Comment: published version, 2 figures added; 21 pages, 3 figure

Asymptotic spectral properties of the Hilbert LL-matrix

We study asymptotic spectral properties of the generalized Hilbert $L$-matrix $$L_{n}(\nu)=\left(\frac{1}{\max(i,j)+\nu}\right)_{i,j=0}^{n-1},$$ for large order $n$. First, for general $\nu\neq0,-1,-2,\dots$, we deduce the asymptotic distribution of eigenvalues of $L_{n}(\nu)$ outside the origin. Second, for $\nu>0$, asymptotic formulas for small eigenvalues of $L_{n}(\nu)$ are derived. Third, in the classical case $\nu=1$, we also prove asymptotic formulas for large eigenvalues of $L_{n}\equiv L_{n}(1)$. I particular, we obtain an asymptotic expansion of $\|L_{n}\|$ improving Wilf's formula for the best constant in truncated Hardy's inequality.Comment: 18 pages, dedicated to the memory of Harold Widom, accepted for publication in SIAM J. Matrix Anal. App