Poster
Truncated Variance Reduced Value Iteration
Yujia Jin · Ishani Karmarkar · Aaron Sidford · Jiayi Wang
West Ballroom A-D #6405
Abstract:
We provide faster randomized algorithms for computing an -optimal policy in a discounted Markov decision process with -state-action pairs, bounded rewards, and discount factor . We provide an -time algorithm in the sampling setting, where the probability transition matrix is unknown but accessible through a generative model which can be queried in -time, and an -time algorithm in the offline setting where the probability transition matrix is known and -sparse. These results improve upon the prior state-of-the-art which either ran in time [Sidford, Wang, Wu, Ye 2018] in the sampling setting, time [Sidford, Wang, Wu, Yang, Ye 2018] in the offline setting, or time at least quadratic in the number of states using interior point methods for linear programming. We achieve our results by building upon prior stochastic variance-reduced value iteration methods [Sidford, Wang, Wu, Yang, Ye 2018]. We provide a variant that carefully truncates the progress of its iterates to improve the variance of new variance-reduced sampling procedures that we introduce to implement the steps. Our method is essentially model-free and can be implemented in -space when given generative model access. Consequently, our results take a step in closing the sample-complexity gap between model-free and model-based methods.
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