Nonsmooth analysis of eigenvalues
The eigenvalues of a symmetric matrix depend on the matrix nonsmoothly. This paper describes the nonsmooth analysis of these eigenvalues. In particular, I present a simple formula for the approximate (limiting Frechet) subdifferential of an arbitrary function of the eigenvalues, subsuming earlier results on convex and Clarke subgradients. As an example I compute the subdifferential of the k'th largest eigenvalue.
nonsmooth analysis clarke subgradient eigenvalue optimization approximate subdifferential generalized derivative horizon subgradient semidefinite program