Portable wireless devices are ubiquitous in modern society and many of these have integral sensors such as accelerometers, microphones, and Global Positioning Systems (GPS) that can collect data. This creates potential for intelligent applications to recognize the user, or aspects of the user and take appropriate action. According to embodiments of the invention there are presented techniques for representing such time series data which reduce the memory and computational complexity of performing the analysis and classifying the results. The techniques exploit time-delay embedding is to reconstruct the state and dynamics of an unknown dynamical system, Geometric Template Matching to build nonparametric classifiers, and algorithms to address the problem of selecting segments of data from which to build the time-delay models for classification problems.