16. Learning Mixtures by Simplifying Kernel Density Estimators

Gaussian mixture models are a widespread tool for modeling various and complex probability density functions. They can be estimated by various means, often using Expectation–Maximization or Kernel Density Estimation. In addition to these well known algorithms, new and promising stochastic modeling methods include Dirichlet Process mixtures and k-Maximum Likelihood Estimators. Most of the methods, including Expectation–Maximization, lead to compact models but may be expensive to compute. On the other hand Kernel Density Estimation yields to large models which are computationally cheap to build. In this chapter we present new methods to get high-quality models that are both compact and fast to compute. This is accomplished by the simplification of Kernel Density Estimator. The simplification is a clustering method based on k-means-like algorithms. Like all k-means algorithms, our method rely on divergences and centroids computation and we use two different divergences (and their associated centroids), Bregman and . Along with the description of the algorithms, we describe the pyMEF =library=, which is a Python library designed for the manipulation of mixture of exponential families. Unlike most of the other existing tools, this library allows to use any exponential family instead of being limited to a particular distribution. The generic library allows to rapidly explore the different available exponential families in order to choose the better suited for a particular application. We evaluate the proposed algorithms by building mixture models on examples from a bio-informatics application. The quality of the resulting models is measured in terms of log-likelihood and of Kullback–Leibler divergence.