New techniques for pairwise symmetry breaking in multi-agent path finding

Abstract

We consider two new classes of pairwise path symmetries which appear in the context of Multi-Agent Path Finding (MAPF). The first of them, corridor symmetry, arises when two agents attempt to pass through the same narrow passage in opposite directions. The second, target symmetry, arises when the shortest path of one agent passes through the target location of a second agent after the second agent has already arrived at it. We propose to break these symmetries using specialized constraints while preserving optimality. We experimentally show that our techniques can significantly speed up Conflict-Based Search, a state-of-the-art MAPF algorithm.