Mustapha Lebbah

GTM Mixture through time for sequential data

Generative Topographic Mapping (GTM) is a popular probabilistic framework for modeling non-linear relationships in high-dimensional data as well as for unsupervised learning and visualization of such data. It is also known as to provide a principled probabilistic alternative to the well-known Self-Organizing Map (SOM) in the neural networks community, thanks to its flexible mixture model formulation and the desirable properties of the expectation-maximization (EM) algorithm. However, much attention has been focused on the use of GTM for multivariate data, in general assumed to be independent and identically distributed (i.i.d) and the problem of modeling sequences using GTM is less investigated. In this paper, we focus on GTM for unsupervised modeling and visualization of sequential data. We consider modeling sequences of continuous multidimensional observations and we propose a GTM through time (GTM-TT) approach based on hidden Markov models (HMM) where the observations are a sent of independent sequences, rather than a signle sequence. We further extend the model to the clustering of multiple sequences by proposing a GTM-TT mixture model. The model parameters are estimated by maximum likelihood via the EM algorithm. The proposed approach is evaluated using simulated data and real-world data.