Training a multi-agent reinforcement learning (MARL) model is generally difficult because there are numerous combinations of complex interactions among agents that induce certain reward signals. Especially when there is a sparse reward signal, the training becomes more difficult. Previous studies have tried to resolve this issue by employing an intrinsic reward, which is a signal specifically designed for inducing the interactions among agents, to boost the MARL model training. However, this approach requires extensive prior knowledge to design an intrinsic reward. To optimize the training of an MARL model, we propose a learning-based exploration strategy to generate the initial states of a game. The proposed method adopts a variational graph autoencoder to represent a state of a game such that (1) the state can be compactly encoded to the latent representation by considering the relationship among agents, and (2) the latent representation can be used as an effective input to the surrogate model predicting the exploration score. The proposed method determines the latent representations that maximize the surrogate model and decodes these representations to generate the initial states from which the MARL model starts training. Empirically, we demonstrate that the generated states improve the training and performance of MARL more than the existing exploration methods.
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