Model-based algorithms, which learn a dynamics model from logged experience and perform some sort of pessimistic planning under the learned model, have emerged as a promising paradigm for offline reinforcement learning (offline RL). However, practical variants of such model-based algorithms rely on explicit uncertainty quantification for incorporating pessimism. Uncertainty estimation with complex models, such as deep neural networks, can be difficult and unreliable. We overcome this limitation by developing a new model-based offline RL algorithm, COMBO, that regularizes the value function on out-of-support state-action tuples generated via rollouts under the learned model. This results in a conservative estimate of the value function for out-of-support state-action tuples, without requiring explicit uncertainty estimation. We theoretically show that our method optimizes a lower bound on the true policy value, that this bound is tighter than that of prior methods, and our approach satisfies a policy improvement guarantee in the offline setting. Through experiments, we find that COMBO consistently performs as well or better as compared to prior offline model-free and model-based methods on widely studied offline RL benchmarks, including image-based tasks.

该研究提出一种新的基于模型的线下强化学习算法（COMBO），该算法不需要显式的不确定性估计，通过对已学习模型下的滚动状态动作元组进行价值函数正则化，从而得到状态动作元组价值函数的保守估计。该方法可以优化真实策略价值的下限，且实验表明与先前的线下模型自由和基于模型的方法相比，COMBO在广泛研究的线下RL基准测试中表现持续改进。

COMBO: 保守的离线基于模型的策略优化