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Hilbert Space Embeddings of Predictive State Representations
Proceedings of the 29th Conference on Uncertainty in Artificial Intelligence, PMLR R11:45-54, 2013.
Abstract
Predictive State Representations (PSRs) are an expressive class of models for controlled stochastic processes. PSRs represent state as a set of predictions of future observable events. Because PSRs are defined entirely in terms of observable data, statistically con- sistent estimates of PSR parameters can be learned efficiently by manipulating moments of observed training data. Most learning al- gorithms for PSRs have assumed that actions and observations are finite with low cardinal- ity. In this paper, we generalize PSRs to in- finite sets of observations and actions, using the recent concept of Hilbert space embed- dings of distributions. The essence is to rep- resent the state as one or more nonparamet- ric conditional embedding operators in a Re- producing Kernel Hilbert Space (RKHS) and leverage recent work in kernel methods to es- timate, predict, and update the representa- tion. We show that these Hilbert space em- beddings of PSRs are able to gracefully han- dle continuous actions and observations, and that our learned models outperform compet- ing system identification algorithms on sev- eral prediction benchmarks.