We develop a general class of Bayesian repulsive Gaussian mixture models that encourage well-separated clusters, aiming at reducing potentially redundant components produced by independent priors for locations (such as the Dirichlet process). The asymptotic results for the posterior distribution of the proposed models are derived, including posterior consistency and posterior contraction rate in the context of nonparametric density estimation. More importantly, we show that compared to the independent prior on the component centers, the repulsive prior introduces additional shrinkage effect on the tail probability of the posterior number of components, which serves as a measurement of the model complexity. In addition, an efficient and easy-to-implement blocked-collapsed Gibbs sampler is developed based on the exchangeable partition distribution and the corresponding urn model. We evaluate the performance and demonstrate the advantages of the proposed model through extensive simulation studies and real data analysis. The R code is available at https://drive.google.com/open?id=0B_zFse0eqxBHZnF5cEhsUFk0cVE.

No abstract

We develop a Bayesian approach called Bayesian projected calibration to address the problem of calibrating an imperfect computer model using observational data from a complex physical system. The calibration parameter and the physical system are parametrized in an identifiable fashion via L 2 -projection. The physical process is assigned a Gaussian process prior, which naturally induces a prior distribution on the calibration parameter through the L 2 -projection constraint. The calibration parameter is estimated through its posterior distribution, which provides a natural and non-asymptotic way for the uncertainty quantification. We provide a rigorous large sample justification for the proposed approach by establishing the asymptotic normality of the posterior of the calibration parameter with the efficient covariance matrix. In addition, two efficient computational algorithms based on stochastic approximation are designed with theoretical guarantees. Through extensive simulation studies and two real-world datasets analyses, we show that the Bayesian projected calibration can accurately estimate the calibration parameters, appropriately calibrate the computer models, and compare favorably to alternative approaches. An R package implementing the Bayesian projected calibration is publicly available at https://drive.google.com/open?id=1Sij0P-g5ocnTeL_qcQ386b-jfBfV-ww_.