Parallel Bayesian Global Optimization of Expensive Functions

TL;DR

This paper introduces a stochastic approximation method for efficiently maximizing the multi-points expected improvement in parallel Bayesian optimization, enabling faster and more effective optimization of expensive functions.

Contribution

It develops an unbiased stochastic gradient estimator for the q-EI and proves convergence of the gradient ascent, improving optimization speed and quality for expensive functions.

Findings

Faster maximization of q-EI compared to high-dimensional integration methods.

Achieves high-quality solutions with fewer function evaluations.

Provides an open-source implementation in MOE.

Abstract

We consider parallel global optimization of derivative-free expensive-to-evaluate functions, and propose an efficient method based on stochastic approximation for implementing a conceptual Bayesian optimization algorithm proposed by Ginsbourger et al. (2007). At the heart of this algorithm is maximizing the information criterion called the "multi-points expected improvement'', or the q-EI. To accomplish this, we use infinitessimal perturbation analysis (IPA) to construct a stochastic gradient estimator and show that this estimator is unbiased. We also show that the stochastic gradient ascent algorithm using the constructed gradient estimator converges to a stationary point of the q-EI surface, and therefore, as the number of multiple starts of the gradient ascent algorithm and the number of steps for each start grow large, the one-step Bayes optimal set of points is recovered. We show in numerical experiments that our method for maximizing the q-EI is faster than methods based on closed-form evaluation using high-dimensional integration, when considering many parallel function evaluations, and is comparable in speed when considering few. We also show that the resulting one-step Bayes optimal algorithm for parallel global optimization finds high-quality solutions with fewer evaluations than a heuristic based on approximately maximizing the q-EI. A high-quality open source implementation of this algorithm is available in the open source Metrics Optimization Engine (MOE).