  Existing multi-agent PPO algorithms lack compatibility with different types
of parameter sharing when extending the theoretical guarantee of PPO to
cooperative multi-agent reinforcement learning (MARL). In this paper, we
propose a novel and versatile multi-agent PPO algorithm for cooperative MARL to
overcome this limitation. Our approach is achieved upon the proposed
full-pipeline paradigm, which establishes multiple parallel optimization
pipelines by employing various equivalent decompositions of the advantage
function. This procedure successfully formulates the interconnections among
agents in a more general manner, i.e., the interconnections among pipelines,
making it compatible with diverse types of parameter sharing. We provide a
solid theoretical foundation for policy improvement and subsequently develop a
practical algorithm called Full-Pipeline PPO (FP3O) by several approximations.
Empirical evaluations on Multi-Agent MuJoCo and StarCraftII tasks demonstrate
that FP3O outperforms other strong baselines and exhibits remarkable
versatility across various parameter-sharing configurations.
