
Finding Approximate POMDP solutions Through Belief Compression
M. Roy, G. Gordon, and S. Thrun.Standard value function approaches to finding policies for Partially Observable Markov Decision Processes (POMDPs) are generally considered to be intractable for large models. The intractability of these algorithms is to a large extent a consequence of computing an exact, optimal policy over the entire belief space. However, in realworld POMDP problems, computing the optimal policy for the full belief space is often unnecessary for good control even for problems with complicated policy classes. The beliefs experienced by the controller often lie near a structured, lowdimensional manifold embedded in the highdimensional belief space. Finding a good approximation to the optimal value function for only this manifold can be much easier than computing the full value function. We introduce a new method for solving largescale POMDPs by reducing the dimensionality of the belief space. We use Exponential family Principal Components Analysis (Collins, Dasgupta, & Schapire, 2002) to represent sparse, highdimensional belief spaces using lowdimensional sets of learned features of the belief state. We then plan only in terms of the lowdimensional belief features. By planning in this lowdimensional space, we can find policies for POMDP models that are orders of magnitude larger than models that can be handled by conventional techniques. We demonstrate the use of this algorithm on a synthetic problem and on mobile robot navigation tasks.
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@ARTICLE{Roy04a, AUTHOR = {Roy, N. and Gordon, G. and Thrun, S.}, TITLE = {Finding Approximate {POMDP} Solutions Through Belief Compression}, JOURNAL = {Journal of Artificial Intelligence Research}, YEAR = {2004}, NOTE = {To appear.} } 