Improved Soft Actor-Critic: Mixing Prioritized Off-Policy Samples With On-Policy Experiences

Soft actor-critic (SAC) is an off-policy actor-critic (AC) reinforcement learning (RL) algorithm, essentially based on entropy regularization. SAC trains a policy by maximizing the trade-off between expected return and entropy (randomness in the policy). It has achieved the state-of-the-art performance on a range of continuous control benchmark tasks, outperforming prior on-policy and off-policy methods. SAC works in an off-policy fashion where data are sampled uniformly from past experiences (stored in a buffer) using which the parameters of the policy and value function networks are updated. We propose certain crucial modifications for boosting the performance of SAC and making it more sample efficient. In our proposed improved SAC (ISAC), we first introduce a new prioritization scheme for selecting better samples from the experience replay (ER) buffer. Second we use a mixture of the prioritized off-policy data with the latest on-policy data for training the policy and value function networks. We compare our approach with the vanilla SAC and some recent variants of SAC and show that our approach outperforms the said algorithmic benchmarks. It is comparatively more stable and sample efficient when tested on a number of continuous control tasks in MuJoCo environments.