Nash equilibrium solutions in multi-agent project scheduling with milestones

This paper addresses a project scheduling environment in which the activities are partitioned among a set of agents. The project owner is interested in completing the project as soon as possible. Therefore, she/he defines rewards and penalties to stimulate the agents to complete the project faster. The project owner offers a per-day reward for early project completion and defines intermediate project milestones to be met within specific due dates, with associated per-day penalties. Each agent can, therefore, decide the duration of her/his activities, taking into account linear activity crashing costs, the reward for early project completion, and the penalty arising from violating milestone due-dates. We consider Nash equilibria, i.e., situations in which no agent has an interest in individually changing the duration of any of her/his activities, and in particular, the problem of finding a minimum-makespan equilibrium. This problem is known to be NP-hard, and in this paper, we (i) propose a new and efficient exact algorithmic approach for finding the minimum-makespan equilibrium and (ii) through an extensive computational campaign we evaluate the role played by milestones in driving the project towards the owner's goal.