Eigenvalue paths arising from matrix paths

It is known (see e.g. [2], [4], [5], [6]) that continuous variations in the entries of a complex square matrix induce continuous variations in its eigenvalues. If such a variation arises from one real parameter alpha is an element of [0, 1], then the eigenvalues follow continuous paths in the complex plane as alpha shifts from 0 to 1. The intent here is to study the nature of these eigenpaths, including their behavior under small perturbations of the matrix variations, as well as the resulting eigenpairings of the matrices that occur at alpha = 0 and alpha = 1. We also give analogs of our results in the setting of monic polynomials. (C) 2021 Elsevier Inc. All rights reserved.