Gaussian process modeling with inequality constraints

Gaussian process modeling is one of the most popular approaches for building a metamodel in the case of expensive numerical simulators. Frequently, the code outputs correspond to physical quantities with a behavior which is known a priori: Chemical concentrations lie between 0 and 1, the output is increasing with respect to some parameter, etc. Several approaches have been proposed to deal with such information. In this paper, we introduce a new framework for incorporating constraints in Gaussian process modeling, including bound, monotonicity and convexity constraints. We also extend this framework to any type of linear constraint. This new methodology mainly relies on conditional expectations of the truncated multinormal distribution. We propose several approximations based on correlation-free assumptions, numerical integration tools and sampling techniques. From a practical point of view, we illustrate how accuracy of Gaussian process predictions can be enhanced with such constraint knowledge. We finally compare all approximate predictors on bound, monotonicity and convexity examples.