We present an algorithm based on posterior sampling (aka Thompson sampling) that achieves near-optimal worst-case regret bounds when the underlying Markov Decision Process (MDP) is communicating with a finite, though unknown, diameter. Our main result is a high probability regret upper bound of $\tilde{O}(D\sqrt{SAT})$ for any communicating MDP with $S$ states, $A$ actions and diameter $D$, when $T\ge S^5A$. Here, regret compares the total reward achieved by the algorithm to the total expected reward of an optimal infinite-horizon undiscounted average reward policy, in time horizon $T$. This result improves over the best previously known upper bound of $\tilde{O}(DS\sqrt{AT})$ achieved by any algorithm in this setting, and matches the dependence on $S$ in the established lower bound of $\Omega(\sqrt{DSAT})$ for this problem. Our techniques involve proving some novel results about the anti-concentration of Dirichlet distribution, which may be of independent interest.

提出了一种基于后验采样的算法，应用于具有有限但未知直径的Markov决策过程中，证明了近最优的最坏情况遗憾上界。这种方法通过证明Dirichlet分布的反集中性，可能具有独立研究价值，并将总奖励与最优无限时维度折扣的平均奖励策略的总期望奖励在时间结构 $T$ 中呈现出紧密的匹配。

强化学习的后验采样：最坏情况的遗憾界