The Reachability Objective in Multi-Agent Path Finding

Multi-Agent Path Finding (MAPF) is the problem of path planning for multiple agents while avoiding collisions. In MAPF, each agent must reach a designated target location and stay there. We consider a different objective: each agent must reach its target, but it may move away afterwards. We call this MAPF with Reachability Objective (MAPF-RO). Despite compelling real-world use cases, few prior works have explicitly studied MAPF-RO. We propose several efficient and complete algorithms for MAPF-RO, based on state-of-the-art MAPF algorithms. Experimental results show that using MAPF-RO algorithms instead of classic MAPF algorithms yields huge benefits in terms of runtime and solvability, solving in some cases problems with 1,000 more agents than baseline approaches. Then, we show a reduction that allows using our MAPF-RO to solve MAPF with Unassigned Agents, a recent practical variant of MAPF in which only a subset of the agents are assigned targets.