Nonconvex Regularized Robust PCA Using the Proximal Block Coordinate Descent Algorithm

This work addresses the robust principal component analysis (PCA) problem using generalized nonoconvex regularization for low-rank and sparsity promotion. While the popular nuclear and l(1)-norm penalties have a bias problem, nonconvex regularization can alleviate the bias problem and can be expected to achieve better performance. In this paper, a proximal block coordinate descent (BCD) algorithm is used to efficiently solve the nonconvex regularized robust PCA problem. It is globally convergent under weak conditions. Further, for a popular class of penalties having discontinuous threshoding functions, we establish the convergence to a restricted strictly local minimizer and, also, a local linear convergence rate for the proximal BCD algorithm. Moreover, convergence to a local minimizer has been derived for hard-thresholding. Our result is the first on nonconvex robust PCA with established convergence to strictly local minimizer with local linear convergence rate. Numerical experiments have been provided to demonstrate the performance of the new algorithm.