  Ad-hoc team cooperation is the problem of cooperating with other players that
have not been seen in the learning process. Recently, this problem has been
considered in the context of Hanabi, which requires cooperation without
explicit communication with the other players. While in self-play strategies
cooperating on reinforcement learning (RL) process has shown success, there is
the problem of failing to cooperate with other unseen agents after the initial
learning is completed. In this paper, we categorize the results of ad-hoc team
cooperation into Failure, Success, and Synergy and analyze the associated
failures. First, we confirm that agents learning via RL converge to one
strategy each, but not necessarily the same strategy and that these agents can
deploy different strategies even though they utilize the same hyperparameters.
Second, we confirm that the larger the behavioral difference, the more
pronounced the failure of ad-hoc team cooperation, as demonstrated using
hierarchical clustering and Pearson correlation. We confirm that such agents
are grouped into distinctly different groups through hierarchical clustering,
such that the correlation between behavioral differences and ad-hoc team
performance is -0.978. Our results improve understanding of key factors to form
successful ad-hoc team cooperation in multi-player games.
