  Bayesian quadrature optimization (BQO) maximizes the expectation of an
expensive black-box integrand taken over a known probability distribution. In
this work, we study BQO under distributional uncertainty in which the
underlying probability distribution is unknown except for a limited set of its
i.i.d. samples. A standard BQO approach maximizes the Monte Carlo estimate of
the true expected objective given the fixed sample set. Though Monte Carlo
estimate is unbiased, it has high variance given a small set of samples; thus
can result in a spurious objective function. We adopt the distributionally
robust optimization perspective to this problem by maximizing the expected
objective under the most adversarial distribution. In particular, we propose a
novel posterior sampling based algorithm, namely distributionally robust BQO
(DRBQO) for this purpose. We demonstrate the empirical effectiveness of our
proposed framework in synthetic and real-world problems, and characterize its
theoretical convergence via Bayesian regret.
