'Why Not This MAPF Plan Instead?' Contrastive Map-based Explanations for Optimal MAPF

Martim Brandão, Yonathan Setiawan

Keywords: multi-agent path finding, MAPF, inverse shortest-paths

TL;DR: A new problem and methods for explaining MAPF plans

Abstract: Multi-Agent Path Finding (MAPF) plans can be very complex to analyze and understand. Recent user studies have shown that explanations would be a welcome tool for MAPF practitioners and developers to better understand plans, as well as to tune map layouts and cost functions. In this paper we formulate two variants of an explanation problem in MAPF that we call contrastive ``map-based explanation''. The problem consists of answering the question ``why don't agents A follow paths P' instead?''---by finding regions of the map that would have to be an obstacle in order for the expected plan to be optimal. We propose three different methods to compute these explanations, and evaluate them quantitatively on a set of benchmark problems that we make publicly available. Motivations for generating this type of explanation are discussed in the paper and include both user understanding of MAPF problems, and designer-aids to guide the improvement of map layouts.