This paper presents the concept of an adaptive safe padding that forces
Reinforcement Learning (RL) to synthesise optimal control policies while
ensuring safety during the learning process. Policies are synthesised to
satisfy a goal, expressed as a temporal logic formula, with maximal
probability. Enforcing the RL agent to stay safe during learning might limit
the exploration, however we show that the proposed architecture is able to
automatically handle the trade-off between efficient progress in exploration
(towards goal satisfaction) and ensuring safety. Theoretical guarantees are
available on the optimality of the synthesised policies and on the convergence
of the learning algorithm. Experimental results are provided to showcase the
performance of the proposed method.Comment: Accepted to AAMAS 2020. arXiv admin note: text overlap with
arXiv:1902.0077