Gradient-based training of Gaussian Mixture Models in High-Dimensional Spaces
Authors: Alexander Gepperth, Benedikt Pfülb
Keywords: GMM, SGD
TL;DR: We present a stochastic gradient descent algorithm for training GMMs in high-dimensional spaces, which performs similarly to the traditional EM procedure but which is much more memory-efficient.
Abstract: We present an approach for efficiently training Gaussian Mixture Models (GMMs) with Stochastic Gradient Descent (SGD) on large amounts of high-dimensional data (e.g., images). In such a scenario, SGD is strongly superior in terms of execution time and memory usage, although it is conceptually more complex than the traditional Expectation-Maximization (EM) algorithm.
For enabling SGD training, we propose three novel ideas:
First, we show that minimizing an upper bound to the GMM log likelihood instead of the full one is feasible and numerically much more stable way in high-dimensional spaces.
Secondly, we propose a new regularizer that prevents SGD from converging to pathological local minima.
And lastly, we present a simple method for enforcing the constraints inherent to GMM training when using SGD.
We also propose an SGD-compatible simplification to the full GMM model based on local principal directions, which avoids excessive memory use in high-dimensional spaces due to quadratic growth of covariance matrices.
Experiments on several standard image datasets show the validity of our approach, and we provide a publicly available TensorFlow implementation.