Iterative Reweighted Singular Value Minimization

In this paper we study general lp regularized unconstrained matrix minimization problems. In particular, we first introduce a class of first-order stationary points for them. And we show that the first-order stationary points introduced in [11] for an lp regularized vector minimization problem are equivalent to those of an lp regularized matrix minimization reformulation. We also establish that any local minimizer of the lp regularized matrix minimization problems must be a first-order stationary point. Moreover, we derive lower bounds for nonzero singular values of the first-order stationary points and hence also of the local minimizers for the lp matrix minimization problems. The iterative reweighted singular value minimization (IRSVM) approaches are then proposed to solve these problems in which each subproblem has a closed-form solution. We show that any accumulation point of the sequence generated by these methods is a firstorder stationary point of the problems. In addition, we study a nonmontone proximal gradient (NPG) method for solving the lp matrix minimization problems and establish its global convergence. Our computational results demonstrate that the IRSVM and NPG methods generally outperform some existing state-of-the-art methods in terms of solution quality and/or speed. Moreover, the IRSVM methods are slightly faster than the NPG method.