CMIX: Causal Value Decomposition for Cooperative Multi-Agent Reinforcement Learning

Value decomposition plays a pivotal role in ensuring effective credit assignment within Multi-Agent Reinforcement Learning (MARL), particularly in cooperative multi-agent tasks where agents are limited to accessing team rewards only. However, existing methods treat the mixing network as a black box, implicitly assuming that neural networks can autonomously extract important information and achieve rational credit assignment during policy learning. This approach not only lacks interpretability but may also prove inefficient in complex scenarios. To enhance the interpretability and rationality of value decomposition, we propose an innovative approach called “Causal Value Decomposition”(CMIX). CMIX employs causal inference-based models, introducing a set of metrics beyond environmental rewards to enhance robustness and model interpretability. Specifically, CMIX establishes intricate relational structures among agents in complex environments and leverages causal relationships between agents and their surroundings to address the credit assignment challenge in MARL. By employing do-calculus, CMIX accurately measures the impact of each agent's actions on environmental states, precisely determining their contribution to the collective reward. This approach not only enhances the interpretability of existing black-box models but also improves the accuracy of credit assignment in multi-agent systems. Moreover, CMIX exhibits high scalability and complements existing value decomposition techniques. Its effectiveness and scalability have been rigorously tested across various settings, including MPE, LBF, and SMAC environments.