Least Squares Policy Evaluation Algorithms with Linear Function Approximation

  • Authors:
  • A. Nedić;D. P. Bertsekas

  • Affiliations:
  • Department of Electrical Engineering and Computer Science, M.I.T., Cambridge, MA 02139;Department of Electrical Engineering and Computer Science, M.I.T., Cambridge, MA 02139

  • Venue:
  • Discrete Event Dynamic Systems
  • Year:
  • 2003

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Abstract

We consider policy evaluation algorithms within the context of infinite-horizon dynamic programming problems with discounted cost. We focus on discrete-time dynamic systems with a large number of states, and we discuss two methods, which use simulation, temporal differences, and linear cost function approximation. The first method is a new gradient-like algorithm involving least-squares subproblems and a diminishing stepsize, which is based on the λ-policy iteration method of Bertsekas and Ioffe. The second method is the LSTD(λ) algorithm recently proposed by Boyan, which for λ=0 coincides with the linear least-squares temporal-difference algorithm of Bradtke and Barto. At present, there is only a convergence result by Bradtke and Barto for the LSTD(0) algorithm. Here, we strengthen this result by showing the convergence of LSTD(λ), with probability 1, for every λ ∈ [0, 1].