Journal
ELECTRONIC JOURNAL OF STATISTICS
Volume 11, Issue 2, Pages 5105-5164Publisher
INST MATHEMATICAL STATISTICS-IMS
DOI: 10.1214/17-EJS1340SI
Keywords
Generative models; implicit models; Markov chain Monte Carlo; approximate Bayesian computation
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Funding
- UK Engineering and Physical Sciences Research Council (EPSRC) [EP/F500385/1, BB/F529254/1]
- UK Biotechnology and Biological Sciences Research Council (BBSRC) [EP/F500385/1, BB/F529254/1]
- UK Medical Research Council (MRC) [EP/F500385/1, BB/F529254/1]
- Engineering and Physical Sciences Research Council [1224527] Funding Source: researchfish
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Many generative models can be expressed as a differentiable function applied to input variables sampled from a known probability distribution. This framework includes both the generative component of learned parametric models such as variational autoencoders and generative adversarial networks, and also procedurally defined simulator models which involve only differentiable operations. Though the distribution on the input variables to such models is known, often the distribution on the output variables is only implicitly defined. We present a method for performing efficient Markov chain Monte Carlo inference in such models when conditioning on observations of the model output. For some models this offers an asymptotically exact inference method where approximate Bayesian computation might otherwise be employed. We use the intuition that computing conditional expectations is equivalent to integrating over a density defined on the manifold corresponding to the set of inputs consistent with the observed outputs. This motivates the use of a constrained variant of Hamiltonian Monte Carlo which leverages the smooth geometry of the manifold to move between inputs exactly consistent with observations. We validate the method by performing inference experiments in a diverse set of models.
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