Eigenvalue location using certain matrix functions and geometric curves

The main inertia theorem gives necessary and sufficient conditions that an n×n complex matrix A have no eigenvalues on the imaginary axis of the complex plane. In this paper corresponding necessary and sufficient conditions are given that A have no eigenvalues on any arbitrary circle, line, and certain other curves in the complex plane. Generalizations of the second part of the main inertia theorem give inclusion regions for the eigenvalues of A.