Meta Learning Task Representation in Multiagent Reinforcement Learning: From Global Inference to Local Inference

Multiagent meta reinforcement learning (MAMRL) enables multiagent systems (MASs) to adapt to multiple tasks. However, partial observability poses a significant challenge by hindering efficient task inference from agents' limited local experiences. To address this, we propose MG2L, a novel algorithm featuring a global-to-local (G2L) training scheme based on mutual information optimization (MIO). We first extend the centralized training and decentralized execution (CTDE) framework to MAMRL, and introduce a multilevel task encoder for joint global and local task inference. Building on this encoder, the MG2L scheme employs tailored loss functions to optimize task representations. For global inference, the MAS learns a centralized global representation by maximizing the MI between the representation and the task context. For local inference, we formulate conditional MI reduction to quantify the G2L gap. Agents then learn the local representation by minimizing this reduction. The MG2L scheme effectively harmonizes centralized training with decentralized execution, offering a versatile solution for MAMRL challenges. Additionally, we integrate a permutation-invariant attention (PIA) module into the task encoder to reduce sensitivity to behavior policy variations. Extensive experiments-including comparative analyses, ablation studies, meta-test evaluations, and visualizations-demonstrate MG2L's effectiveness. The implementation of MG2L is publicly available at https://github.com/zhaozijie2022/mg2l.