Efficient Heterogeneous Exploration with Mutual Policy Divergence Maximization for Multiagent Reinforcement Learning.
Although Multi-Agent Reinforcement Learning (MARL) has achieved notable success in cooperative tasks, many existing methods struggle to generalize to heterogeneous scenarios, where diversified specialization is required. In such tasks, a common way is to disable parameter sharing among agents, but this alone fails to induce sufficient behavioral specialization. To address this limitation, sequential updating schemes have recently been proposed, where agents are updated one by one based on the behaviors of their predecessors. However, exploration strategies tailored to the sequential setting remain underexplored, leaving untapped potential in utilizing the information flow between agents. In this work, we propose to leverage the sequential access to predecessor information to explicitly enhance both exploration efficiency and policy heterogeneity. We introduce a novel MARL framework, Multi-Agent Divergence Policy Optimization (MADPO) with Mutual Policy Divergence Maximization (Mutual PDM). The proposed Mutual PDM consists of two key components, the intra-agent PDM and the inter-agent PDM. The former one encourages each agent to explore novel behaviors by deviating from its own previous policies across episodes, while the latter one promotes behavioral heterogeneity between the current agent and its predecessors. To improve the stability and directionality of the divergence signals, we employ the Conditional Cauchy-Schwarz (CCS) divergence for Mutual PDM. Further, we propose a new extension of CCS divergence for measuring policy divergence of more than two agents, the Generalized Conditional Cauchy-Schwarz (GCCS) divergence. Our GCCS divergence can guide agents with more informative incentives, and enhance the global heterogenization with multiple policies. We theoretically prove that the proposed two divergences can offer a stable entropy-guided incentive for exploration and heterogenization. We empirically demonstrate the connection between overall performance and policy heterogeneity in heterogeneous MARL. Extensive experiments on three challenging MARL benchmarks with over 25 heterogeneous scenarios demonstrate that MADPO consistently outperforms existing state-of-the-art sequential up dating methods in terms of both overall performance and agent heterogeneity.