 
Summary: 1
On an Inverse Eigenvalue Problem for Unitary Hessenberg Matrices
Gregory S. Ammar
Department of Mathematical Sciences
Northern Illinois University
DeKalb, IL 60115 USA
and
Chunyang He
Fachbereich Mathematik
Technische Universit¨at ChemnitzZwickau
PSF 964
O9010 Chemnitz, Germany
ABSTRACT
We show that a unitary upper Hessenberg matrix with positive subdiago
nal elements is uniquely determined by its eigenvalues and the eigenvalues of a
modified principal submatrix. This provides an analog of a wellknown result for
Jacobi matrices.
1. INTRODUCTION
We refer to a real symmetric tridiagonal matrix with positive subdiagonal
entries as a Jacobi matrix. Jacobi matrices are closely connected with
