Eigenvalue Paths Arising From Matrix Paths

Abstract: 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 $\alpha \in [0, 1]$, 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.