DEFENDER: DTW-Based Episode Filtering Using Demonstrations for Enhancing
  RL Safety
André Correia Luís Alexandre
Deploying reinforcement learning agents in the real world can be challenging
due to the risks associated with learning through trial and error. We propose a
task-agnostic method that leverages small sets of safe and unsafe
demonstrations to improve the safety of RL agents during learning. The method
compares the current trajectory of the agent with both sets of demonstrations
at every step, and filters the trajectory if it resembles the unsafe
demonstrations. We perform ablation studies on different filtering strategies
and investigate the impact of the number of demonstrations on performance. Our
method is compatible with any stand-alone RL algorithm and can be applied to
any task. We evaluate our method on three tasks from OpenAI Gym's Mujoco
benchmark and two state-of-the-art RL algorithms. The results demonstrate that
our method significantly reduces the crash rate of the agent while converging
to, and in most cases even improving, the performance of the stand-alone agent.