Projection-Free Non-Smooth Convex Programming

Abstract: In this paper, we provide a sub-gradient based algorithm to solve general constrained convex optimization without taking projections onto the domain set. The well studied Frank-Wolfe type algorithms also avoid projections. However, they are only designed to handle smooth objective functions. The proposed algorithm treats both smooth and non-smooth problems and achieves an $O(1/\sqrt{T})$ convergence rate (which matches existing lower bounds). The algorithm yields similar performance in expectation when the deterministic sub-gradients are replaced by stochastic sub-gradients. Thus, the proposed algorithm is a projection-free alternative to the Projected sub-Gradient Descent (PGD) and Stochastic projected sub-Gradient Descent (SGD) algorithms.