Gradientless Descent: High-Dimensional Zeroth-Order Optimization
February 12, 2020 (NSH 3305)

Zeroth-order optimization is the process of minimizing an objective f(x), given oracle access to evaluations at adaptively chosen inputs x. In this paper, we present two simple yet powerful GradientLess Descent (GLD) algorithms that do not rely on an underlying gradient estimate and are numerically stable. We analyze our algorithm from a novel geometric perspective and present a novel analysis that shows convergence within an -ball of the optimum in O(kQ log(n) log(R/ )) evaluations, for any monotone transform of a smooth and strongly convex objective with latent dimension k < n, where the input dimension is n, R is the diameter of the input space and Q is the condition number. Our rates are the first of its kind to be both 1) poly-logarithmically dependent on dimensionality and 2) invariant under monotone transformations. We further leverage our geometric perspective to show that our analysis is optimal.