A new relative perturbation theorem for singular subspaces

Abstract

This note addresses the sensitivity of singular subspaces of a matrix under relative perturbations. It employs a new technique of separating a multiplicative perturbation D into two components: one is the distance of a scalar multiple of D to the nearest unitary matrix Q and the other is the distance of Q to the identity. Consequently, the new bounds reflect the intrinsic differences in how left and right multiplicative perturbations affect left and right singular subspaces.