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Title: Support-guided Adversarial Imitation Learning

Paper content:
We propose Support-guided Adversarial Imitation Learning (SAIL), a generic imitation learning framework that unifies support estimation of the expert policy with the family of Adversarial Imitation Learning (AIL) algorithms.
SAIL addresses two important challenges of AIL, including the implicit reward bias and potential training instability.
We also show that SAIL is at least as efficient as standard AIL.
In an extensive evaluation, we demonstrate that the proposed method effectively handles the reward bias and achieves better performance and training stability than other baseline methods on a wide range of benchmark control tasks.
The class of Adversarial Imitation Learning (AIL) algorithms learns robust policies that imitate an expert's actions from a small number of expert trajectories, without further access to the expert or environment signals.
AIL iterates between refining a reward via adversarial training, and reinforcement learning (RL) with the learned adversarial reward.
For instance, Generative Adversarial Imitation Learning (GAIL) (Ho & Ermon, 2016) shows the equivalence between some settings of inverse reinforcement learning and Generative Adversarial Networks (GANs) (Goodfellow et al., 2014) , and recasts imitation learning as distribution matching between the expert and the RL agent.
Similarly, Adversarial Inverse Reinforcement Learning (AIRL) (Fu et al., 2017) modifies the GAIL discriminator to learn a reward function robust to changes in dynamics or environment properties.
AIL mitigates the issue of distributional drift from behavioral cloning (Ross et al., 2011) , a classical imitation learning algorithm, and demonstrates good performance with only a small number of expert demonstrations.
However, AIL has several important challenges, including implicit reward bias (Kostrikov et al., 2019) , potential training instability (Salimans et al., 2016; Brock et al., 2018) , and potential sample inefficiency with respect to environment interaction (Sasaki et al., 2019) .
In this paper, we propose a principled approach towards addressing these issues.
Wang et al. (2019) demonstrated that imitation learning is also feasible by constructing a fixed reward function via estimating the support of the expert policy.
Since support estimation only requires expert demonstrations, the method sidesteps the training instability associated with adversarial training.
However, we show in Section 4.2 that the reward learned via support estimation deteriorates when expert data is sparse, and leads to poor policy performances.
Support estimation and adversarial reward represent two different yet complementary RL signals for imitation learning, both learnable from expert demonstrations.
We unify both signals into Supportguided Adversarial Imitation Learning (SAIL), a generic imitation learning framework.
SAIL leverages the adversarial reward to guide policy exploration and constrains the policy search to the estimated support of the expert policy.
It is compatible with existing AIL algorithms, such as GAIL and AIRL.
We also show that SAIL is at least as efficient as standard AIL.
In an extensive evaluation, we demonstrate that SAIL mitigates the implicit reward bias and achieves better performance and training stability against baseline methods over a series of benchmark control tasks.
In this paper, we propose Support-guided Adversarial Imitation Learning by combining support guidance with adversarial imitation learning.
Our approach is complementary to existing adversarial imitation learning algorithms, and addresses several challenges associated with them.
More broadly, our results show that expert demonstrations contain rich sources of information for imitation learning.
Effectively combining different sources of reinforcement learning signals from the expert demonstrations produces more efficient and stable algorithms by constraining the policy search space; and appears to be a promising direction for future research.
10413.1 ± 47.0 RED and SAIL use RND Burda et al. (2018) for support estimation.
We use the default networks from RED 4 .
We set σ following the heuristic in Wang et al. (2019) that (s, a) from the expert trajectories mostly have reward close to 1.

assistant: text: We unify support estimation with the family of Adversarial Imitation Learning algorithms into Support-guided Adversarial Imitation Learning, a more robust and stable imitation learning framework.