HYPERDIFFERENTIAL SENSITIVITY ANALYSIS WITH RESPECT TO MODEL DISCREPANCY: PRIOR DISTRIBUTIONS

Hyperdifferential sensitivity analysis with respect to model discrepancy was recently developed to enable uncertainty quantification for optimization problems. The approach consists of two primary steps: (i) Bayesian calibration of the discrepancy between high- and low-fidelity models, and (ii) propagating the model discrepancy uncertainty through the optimization problem. When high-fidelity model evaluations are limited, as is common in practice, the prior discrepancy distribution plays a crucial role in the uncertainty analysis. However, specification of this prior is challenging due to its mathematical complexity and many hyperparameters. This article presents a novel approach to specify the prior distribution. Our approach consists of two parts: (1) an algorithmic initialization of the prior hyperparameters that uses existing data to initialize a hyperparameter estimate, and (2) a visualization framework to systematically explore properties of the prior and guide tuning of the hyperparameters to ensure that the prior captures the appropriate range of uncertainty. We provide detailed mathematical analysis and a collection of numerical examples that elucidate properties of the prior that are crucial to ensure uncertainty quantification.