Introducing Delays in Multi-Agent Path Finding

TL;DR

This paper introduces a delay-based approach to handle agent delays in multi-agent pathfinding, avoiding replanning and demonstrating practical efficiency and effectiveness over existing heuristics.

Contribution

It proposes a novel delay introduction method for MAPF that avoids replanning, with proven APX-Hardness and practical solutions using Conflict-Based Search.

Findings

Optimal delay introduction can be found efficiently with Conflict-Based Search.

The method often outperforms state-of-the-art replanning heuristics.

Planning time and plan length are comparable or better than existing methods.

Abstract

We consider a Multi-Agent Path Finding (MAPF) setting where agents have been assigned a plan, but during its execution some agents are delayed. Instead of replanning from scratch when such a delay occurs, we propose delay introduction, whereby we delay some additional agents so that the remainder of the plan can be executed safely. We show that finding the minimum number of additional delays is APX-Hard, i.e., it is NP-Hard to find a $(1+\varepsilon)$-approximation for some $\varepsilon>0$. However, in practice we can find optimal delay-introductions using Conflict-Based Search for very large numbers of agents, and both planning time and the resulting length of the plan are comparable, and sometimes outperform the state-of-the-art heuristics for replanning.