EP-based infinite inverted dirichlet mixture learning: Application to image spam detection

Abstract

We propose in this paper a new fully unsupervised model based on a Dirichlet process prior and the inverted Dirichlet distribution that allows the automatic inferring of clusters from data. The main idea is to let the number of mixture components increases as new vectors arrive. This allows answering the model selection problem in a elegant way since the resulting model can be viewed as an infinite inverted Dirichlet mixture. An expectation propagation (EP) inference methodology is developed to learn this model by obtaining a full posterior distribution on its parameters. We validate the model on a challenging application namely image spam filtering to show the merits of the framework.