Probabilistic Policy Reuse for Safe Reinforcement Learning

This work introduces Policy Reuse for Safe Reinforcement Learning, an algorithm that combines Probabilistic Policy Reuse and teacher advice for safe exploration in dangerous and continuous state and action reinforcement learning problems in which the dynamic behavior is reasonably smooth and the space is Euclidean. The algorithm uses a continuously increasing monotonic risk function that allows for the identification of the probability to end up in failure from a given state. Such a risk function is defined in terms of how far such a state is from the state space known by the learning agent. Probabilistic Policy Reuse is used to safely balance the exploitation of actual learned knowledge, the exploration of new actions, and the request of teacher advice in parts of the state space considered dangerous. Specifically, the π-reuse exploration strategy is used. Using experiments in the helicopter hover task and a business management problem, we show that the π-reuse exploration strategy can be used to completely avoid the visit to undesirable situations while maintaining the performance (in terms of the classical long-term accumulated reward) of the final policy achieved.