Cross-Entropy Method (CEM) is commonly used for planning in model-based reinforcement learning (MBRL) where a centralized approach is typically utilized to update the sampling distribution based on only the top-k operations' results on samples. In this paper, we show that such a centralized approach makes CEM vulnerable to local optima, thus impairing its sample efficiency. To tackle this issue, we propose Decentralized CEM (DecentCEM), a simple but effective improvement over classical CEM, by using an ensemble of CEM instances running independently from one another, and each performing a local improvement of its own sampling distribution. We provide both theoretical and empirical analysis to demonstrate the effectiveness of this simple decentralized approach. We empirically show that, compared to the classical centralized approach using either a single or even a mixture of Gaussian distributions, our DecentCEM finds the global optimum much more consistently thus improves the sample efficiency. Furthermore, we plug in our DecentCEM in the planning problem of MBRL, and evaluate our approach in several continuous control environments, with comparison to the stateof-art CEM based MBRL approaches (PETS and POPLIN). Results show sample efficiency improvement by simply replacing the classical CEM module with our DecentCEM module, while only sacrificing a reasonable amount of computational cost. Lastly, we conduct ablation studies for more in-depth analysis.

Attention over learned object embeddings enables complex visual reasoning.

DrQ: This model-free, off-policy reinforcement learning algorithm, is based on Soft Actor-Critic (SAC) [19]. DrQ enhances training stability via applying data augmentation to regularize the Q value of state-action pairs. The key of DrQ is to promote similarity between augmented state-action pairs. The Q-regularization technique is shown in Eq 1, where K is the number of samples, T is the collection of augmentation. Q(f (s,νk),ak) where νk T and ak π( | f (s,νk)) (1) DrQ-v2: An improved version of DrQ. DrQ-v2 fuses essential elements from the DDPG algorithm with data augmentation to strengthen visual RL agents' performance. DrQ-v2 also incorporates techniques such as n-step return and target critic, leading to commendable results in most of the medium and hard level DM-Control tasks. The auxiliary contrastive loss (Eq 3) allows the agent to obtain better image representation during training, thus mitigating the optimization difficulty under high-dimensional inputs.

Temporal abstraction in reinforcement learning (RL), offers the promise of improving generalization and knowledge transfer in complex environments, by propagating information more efficiently over time. Although option learning was initially formulated in a way that allows updating many options simultaneously, using off-policy, intra-option learning (Sutton, Precup & Singh, 1999), many of the recent hierarchical reinforcement learning approaches only update a single option at a time: the option currently executing. We revisit and extend intra-option learning in the context of deep reinforcement learning, in order to enable updating all options consistent with current primitive action choices, without introducing any additional estimates. Our method can therefore be naturally adopted in most hierarchical RL frameworks. When we combine our approach with the option-critic algorithm for option discovery, we obtain significant improvements in performance and data-efficiency across a wide variety of domains.