  Imitation Learning (IL) methods seek to match the behavior of an agent with
that of an expert. In the present work, we propose a new IL method based on a
conceptually simple algorithm: Primal Wasserstein Imitation Learning (PWIL),
which ties to the primal form of the Wasserstein distance between the expert
and the agent state-action distributions. We present a reward function which is
derived offline, as opposed to recent adversarial IL algorithms that learn a
reward function through interactions with the environment, and which requires
little fine-tuning. We show that we can recover expert behavior on a variety of
continuous control tasks of the MuJoCo domain in a sample efficient manner in
terms of agent interactions and of expert interactions with the environment.
Finally, we show that the behavior of the agent we train matches the behavior
of the expert with the Wasserstein distance, rather than the commonly used
proxy of performance.
