Spectral characterizations and integer powers of tridiagonal 2-Toeplitz matrices

Abstract

In this note, we consider real nonsymmetric tridiagonal 2-Toeplitz matrices \(\textbf{B}_n\). First we give the asymptotic spectral and singular value distribution of the whole matrix-sequence \(\{\textbf{B}_n\}_n\), which is described via two eigenvalue functions of a \(2\times 2\) matrix-valued symbol. In connection with the above findings, we provide a characterization of the eigenvalues and eigenvectors of real tridiagonal 2-Toeplitz matrices \(\textbf{B}_n\) of even order, that can be turned into a numerical effective scheme for the computation of all the entries of \(\textbf{B}_n^l\), n even and l positive and small compared to n. We recall that a corresponding eigenvalue decomposition for odd order tridiagonal 2-Toeplitz matrices was found previously, while, for even orders, an implicit formula for all the eigenvalues is obtained.