Safe state abstraction and reusable continuing subtasks in hierarchical reinforcement learning

Hierarchical reinforcement learning methods have not been able to simultaneously abstract and reuse subtasks with discounted value functions. The contribution of this paper is to introduce two completion functions that jointly decompose the value function hierarchically to solve this problem. The significance of this result is that the benefits of hierarchical reinforcement learning can be extended to discounted value functions and to continuing (infinite horizon) reinforcement learning problems. This paper demonstrates the method with the an algorithm that discovers subtasks automatically. An example is given where the optimum policy requires a subtask never to terminate.