Title: A unified view of entropy-regularized Markov decision processes,
Abstract: We propose a general framework for entropy-regularized average-reward
reinforcement learning in Markov decision processes (MDPs). Our approach is
based on extending the linear-programming formulation of policy optimization in
MDPs to accommodate convex regularization functions. Our key result is showing
that using the conditional entropy of the joint state-action distributions as
regularization yields a dual optimization problem closely resembling the
Bellman optimality equations. This result enables us to formalize a number of
state-of-the-art entropy-regularized reinforcement learning algorithms as
approximate variants of Mirror Descent or Dual Averaging, and thus to argue
about the convergence properties of these methods. In particular, we show that
the exact version of the TRPO algorithm of Schulman et al. (2015) actually
converges to the optimal policy, while the entropy-regularized policy gradient
methods of Mnih et al. (2016) may fail to converge to a fixed point. Finally,
we illustrate empirically the effects of using various regularization
techniques on learning performance in a simple reinforcement learning setup.