  Agents trained with deep reinforcement learning algorithms are capable of
performing highly complex tasks including locomotion in continuous
environments. We investigate transferring the learning acquired in one task to
a set of previously unseen tasks. Generalization and overfitting in deep
reinforcement learning are not commonly addressed in current transfer learning
research. Conducting a comparative analysis without an intermediate
regularization step results in underperforming benchmarks and inaccurate
algorithm comparisons due to rudimentary assessments. In this study, we propose
regularization techniques in deep reinforcement learning for continuous control
through the application of sample elimination, early stopping and maximum
entropy regularized adversarial learning. First, the importance of the
inclusion of training iteration number to the hyperparameters in deep transfer
reinforcement learning will be discussed. Because source task performance is
not indicative of the generalization capacity of the algorithm, we start by
acknowledging the training iteration number as a hyperparameter. In line with
this, we introduce an additional step of resorting to earlier snapshots of
policy parameters to prevent overfitting to the source task. Then, to generate
robust policies, we discard the samples that lead to overfitting via a method
we call strict clipping. Furthermore, we increase the generalization capacity
in widely used transfer learning benchmarks by using maximum entropy
regularization, different critic methods, and curriculum learning in an
adversarial setup. Subsequently, we propose maximum entropy adversarial
reinforcement learning to increase the domain randomization. Finally, we
evaluate the robustness of these methods on simulated robots in target
environments where the morphology of the robot, gravity, and tangential
friction coefficient of the environment are altered.
