Q-Tree: automatic construction of hierarchical state representation for reinforcement learning

  • Authors:
  • Tao Mao;Zhao Cheng;Laura E. Ray

  • Affiliations:
  • Thayer School of Engineering, Dartmouth Collge, NH;Thayer School of Engineering, Dartmouth Collge, NH;Thayer School of Engineering, Dartmouth Collge, NH

  • Venue:
  • ICIRA'12 Proceedings of the 5th international conference on Intelligent Robotics and Applications - Volume Part III
  • Year:
  • 2012

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Abstract

A primary challenge of agent-based reinforcement learning in complex and uncertain environments is escalating computational complexity with the number of the states. Hierarchical, or tree-based, state representation provides a promising approach to complexity reduction through clustering and sequencing of similar states. We introduce the Q-Tree algorithm to utilize the data history of state transition information to automatically construct such a representation and to obtain a series of linear separations between state clusters to facilitate learning. Empirical results for the canonical PuddleWorld problem are provided to validate the proposed algorithm; extensions of the PuddleWorld problem obtained by adding random noise dimensions are solved by the Q-Tree algorithm, while traditional tabular Q-learning cannot accommodate random state elements within the same number of learning trials. The results show that the Q-Tree algorithm can reject state dimensions that do not aid learning by analyzing weights of all linear classifiers for a hierarchical state representation.