Hierarchical Policy Gradient Algorithms

Mohammad Ghavamzadeh, University of Massachusetts - Amherst
Sridhar Mahadevan, University of Massachusetts - Amherst

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Abstract

Hierarchical reinforcement learning is a general framework which attempts to accelerate policy learning in large domains. On the other hand, policy gradient reinforcement learning (PGRL) methods have received recent attention as a means to solve problems with continuous state spaces. However, they suer from slow convergence. In this paper, we combine these two approaches and propose a family of hierarchical policy gradi- ent algorithms for problems with continuous state and/or action spaces. We also introduce a class of hierarchical hybrid algorithms, in which a group of subtasks, usually at the higher-levels of the hierarchy, are formulated as value function-based RL (VFRL) problems and the others as PGRL problems. We demonstrate the performance of our proposed algorithms using a simple taxi-fuel problem and a complex continuous state and action ship steering domain.