Spectrum through pseudospectrum

Abstract

We present an iteration for the computation of simple eigenvalues using a pseudospectrum approach. The most appealing characteristic of the proposed iteration is that it reduces the computation of a single eigenvalue to a small number of eigenvalue computations on Hermitian matrices. We show that this number is directly associated with the matrix pseudospectrum. We present numerical results and we discuss advantages and drawbacks of the method. We also discuss its relationship with an iteration that was proposed independently in [Stewart, O' Leary, ETNA, Vol 8, 1998].