Exponential-Family Harmoniums with Neural Sufficient Statistics

Azwar Abdulsalam, Joseph G. Makin

Abstract: Exponential-family harmoniums (EFHs) generalize the restricted Boltzmann machine beyond Bernoulli random variables to other exponential families. Here we show how to extend the EFH beyond standard exponential families (Poisson, Gaussian, etc.), by allowing the sufficient statistics for the hidden units to be arbitrary functions of the observed data, parameterized by deep neural networks. This rules out the standard sampling scheme, block Gibbs sampling, so we replace it with a form of Langevin dynamics within Gibbs, inspired by a recent method for training Gaussian restricted Boltzmann machines (GRBMs). With Gibbs-Langevin, the GRBM can successfully model small datasets like MNIST and CelebA-32, but struggles with CIFAR-10, and cannot scale to larger images because it lacks convolutions. In contrast, our neural-network EFHs (NN-EFHs) generate high-quality samples from CIFAR-10 and scale well to CelebA-HQ. On these datasets, the NN-EFH achieves FID scores that are 25--50% lower than a standard energy-based model with a similar neural-network architecture and the same number of parameters; and competitive with noise-conditional score networks, which utilize more complex neural networks (U-nets) and require considerably more sampling steps.