Eigenvalues of tridiagonal Hermitian Toeplitz matrices with perturbations in the off-diagonal corners

Abstract

In this paper we study the eigenvalues of Hermitian Toeplitz matrices with the entries $2,-1,0,\dots ,0,-\alpha$ in the first column. Notice that the generating symbol depends on the order $n$ of the matrix. If $|\alpha |\le 1$, then the eigenvalues belong to $[0,4]$ and are asymptotically distributed as the function $g(x)=4{\sin }^2(x/2)$ on $[0,\pi ]$. The situation changes drastically when $|\alpha |>1$ and $n$ tends to infinity. Then the two extreme eigenvalues (the minimal and the maximal one) lay out of $[0,4]$ and converge rapidly to certain limits determined by the value of $\alpha$, whilst all others belong to $[0,4]$ and are asymptotically distributed as $g$. In all cases, we transform the characteristic equation to a form convenient to solve by numerical methods, and derive asymptotic formulas for the eigenvalues.

22 pages, 4 figures

References in corpus (1)

• Cofactors and eigenvectors of banded Toeplitz matrices: Trench formulas via skew Schur polynomials