We consider the Multi-Armed Bandit (MAB) problem, where the agent sequentially chooses actions and observes rewards for the actions it took. While the majority of algorithms try to minimize the regret. i.e., the cumulative difference between the reward of the best action and the agent's action, this criterion might lead to undesirable results. For example, in large problems, or when the interaction with the environment is brief, finding an optimal arm is infeasible, and regret-minimizing algorithms tend to over-explore. To overcome this issue, algorithms for such settings should instead focus on playing near-optimal arms. To this end, we suggest a new, more lenient, regret criterion that ignores suboptimality gaps smaller than some $\epsilon$. We then present a variant of the Thompson Sampling (TS) algorithm, called $\epsilon$-TS, and prove its asymptotic optimality in terms of the lenient regret. Importantly, we show that when the mean of the optimal arm is high enough, the lenient regret of $\epsilon$-TS is bounded by a constant. Finally, we show that $\epsilon$-TS can be applied to improve the performance when the agent knows a lower bound of the suboptimality gaps.

本文提出了一种忽略一定程度下最优性差距的Bandit算法，并以其为基础，设计优化算法Thompson Sampling(ε-TS)。研究结果表明，该算法能够在一定程度上避免过度探索问题，并在保证性能的前提下，提高计算效率。

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