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Minimax Bounds on Stochastic Batched Convex Optimization
Proceedings of the 31st Conference On Learning Theory, PMLR 75:3065-3162, 2018.
Abstract
We study the stochastic batched convex optimization problem, in which we use many \emph{parallel} observations to optimize a convex function given limited rounds of interaction. In each of M rounds, an algorithm may query for information at n points, and after issuing all n queries, it receives unbiased noisy function and/or (sub)gradient evaluations at the n points. After M such rounds, the algorithm must output an estimator. We provide lower and upper bounds on the performance of such batched convex optimization algorithms in zeroth and first-order settings for Lipschitz convex and smooth strongly convex functions. Our rates of convergence (nearly) achieve the fully sequential rate once M=O(dloglogn), where d is the problem dimension, but the rates may exponentially degrade as the dimension d increases, in distinction from fully sequential settings.