Coalition formation is concerned with the question of how to partition a set of agents into disjoint coalitions according to their preferences. Deviating from most of the previous work, we consider an online variant of the problem, where agents arrive in sequence. Whenever an agent arrives, they must be assigned to a coalition immediately and irrevocably. The scarce existing literature on online coalition formation has focused on maximizing social welfare, a demanding requirement, even in the offline setting. Instead, we seek to achieve \emph{stable} coalition structures online and treat the most common stability concepts based on deviations by single agents and groups of agents. We present a comprehensive picture in additively separable hedonic games, leading to dichotomies, where positive results are obtained by deterministic algorithms and negative results even hold for randomized algorithms.

翻译：联盟形成关注如何根据代理人的偏好将一组代理人划分为不相交的联盟。与以往大多数研究不同，我们考虑该问题的一个在线变体，其中代理人按顺序到达。每当一个代理人到达时，必须立即且不可撤销地将其分配到一个联盟。现有关于在线联盟形成的有限文献主要集中于最大化社会福利，这是一个即使在离线设置下也要求苛刻的目标。相反，我们寻求在线实现\emph{稳定的}联盟结构，并处理基于单个代理人和代理人群体偏离的最常见稳定性概念。我们在可加可分离的享乐博弈中给出了一个全面的图景，导致了二分法的结果，其中正面结果由确定性算法获得，而负面结果甚至对随机算法也成立。