Posterior Sampling-Based Bayesian Optimization with Tighter Bayesian Regret Bounds
This work addresses incremental improvements in Bayesian optimization for researchers and practitioners by providing theoretical guarantees and practical solutions for acquisition function selection.
The paper tackles the problem of improving Bayesian optimization by analyzing acquisition functions, showing that Thompson sampling and a new variant called PIMS achieve tighter Bayesian cumulative regret bounds, with PIMS also avoiding hyperparameter tuning and mitigating over-exploration issues in experiments.
Among various acquisition functions (AFs) in Bayesian optimization (BO), Gaussian process upper confidence bound (GP-UCB) and Thompson sampling (TS) are well-known options with established theoretical properties regarding Bayesian cumulative regret (BCR). Recently, it has been shown that a randomized variant of GP-UCB achieves a tighter BCR bound compared with GP-UCB, which we call the tighter BCR bound for brevity. Inspired by this study, this paper first shows that TS achieves the tighter BCR bound. On the other hand, GP-UCB and TS often practically suffer from manual hyperparameter tuning and over-exploration issues, respectively. Therefore, we analyze yet another AF called a probability of improvement from the maximum of a sample path (PIMS). We show that PIMS achieves the tighter BCR bound and avoids the hyperparameter tuning, unlike GP-UCB. Furthermore, we demonstrate a wide range of experiments, focusing on the effectiveness of PIMS that mitigates the practical issues of GP-UCB and TS.