Overlapping coalition formation games: Charting the tractability frontier

Cooperative games with overlapping coalitions (OCF games) [3, 23] model scenarios where agents can distribute their resources among several tasks; each task generates a profit which may be freely divided among the agents participating in the task. The goal of this work is to initiate a systematic investigation of algorithmic aspects of OCF games. We propose a discretized model of overlapping coalition formation, where each agent i ∈ N has a weight w_i ∈ ℕ and may allocate an integer amount of weight to any task. Within this framework, we focus on the computation of outcomes that are socially optimal and/or stable. We discover that the algorithmic complexity of the associated problems crucially depends on the amount of resources that each agent possesses, the maximum coalition size, and the pattern of interaction among the agents. We identify several constraints that lead to tractable subclasses of OCF games, and provide efficient algorithms for games that belong to these subclasses. We supplement our tractability results by hardness proofs, which clarify the role of our constraints.