Trust Region Bounds for Decentralized PPO Under Non-Stationarity

Mingfei Sun, Sam Devlin, Jacob Beck, Katja Hofmann, Shimon Whiteson

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review


We present trust region bounds for optimizing decentralized policies in cooperative Multi-Agent Reinforcement Learning (MARL), which holds even when the transition dynamics are non-stationary. This new analysis provides a theoretical understanding of the strong performance of two recent actor-critic methods for MARL, which both rely on independent ratios, i.e., computing probability ratios separately for each agent's policy. We show that, despite the non-stationarity that independent ratios cause, a monotonic improvement guarantee still arises as a result of enforcing the trust region constraint over all decentralized policies. We also show this trust region constraint can be effectively enforced in a principled way by bounding independent ratios based on the number of agents in training, providing a theoretical foundation for proximal ratio clipping. Finally, our empirical results support the hypothesis that the strong performance of IPPO and MAPPO is a direct result of enforcing such a trust region constraint via clipping in centralized training, and tuning the hyperparameters with regards to the number of agents, as predicted by our theoretical analysis.
Original languageEnglish
Title of host publicationProceedings of the 2023 International Conference on Autonomous Agents and Multiagent Systems
Place of PublicationRichland, SC
PublisherInternational Foundation for Autonomous Agents and Multiagent Systems
ISBN (Print)9781450394321
Publication statusE-pub ahead of print - 30 May 2023

Publication series

NameAAMAS '23
PublisherInternational Foundation for Autonomous Agents and Multiagent Systems


  • non-stationarity
  • deep reinforcement learning
  • multi-agent systems


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