DBsurf: A Discrepancy Based Method for Discrete Stochastic Gradient
  Estimation
Pau Mulet Arabi Alec Flowers Lukas Mauch Fabien Cardinaux
Computing gradients of an expectation with respect to the distributional
parameters of a discrete distribution is a problem arising in many fields of
science and engineering. Typically, this problem is tackled using Reinforce,
which frames the problem of gradient estimation as a Monte Carlo simulation.
Unfortunately, the Reinforce estimator is especially sensitive to discrepancies
between the true probability distribution and the drawn samples, a common issue
in low sampling regimes that results in inaccurate gradient estimates. In this
paper, we introduce DBsurf, a reinforce-based estimator for discrete
distributions that uses a novel sampling procedure to reduce the discrepancy
between the samples and the actual distribution. To assess the performance of
our estimator, we subject it to a diverse set of tasks. Among existing
estimators, DBsurf attains the lowest variance in a least squares problem
commonly used in the literature for benchmarking. Furthermore, DBsurf achieves
the best results for training variational auto-encoders (VAE) across different
datasets and sampling setups. Finally, we apply DBsurf to build a simple and
efficient Neural Architecture Search (NAS) algorithm with state-of-the-art
performance.