Lifelong Learner: Discovering Versatile Neural Solvers for Vehicle Routing Problems

TL;DR

This paper introduces a lifelong learning framework using Transformer networks to develop versatile neural solvers for vehicle routing problems, capable of adapting across different contexts and outperforming existing methods.

Contribution

It proposes a novel lifelong learning approach with inter-context self-attention and dynamic context scheduling to enhance neural solver versatility for VRPs.

Findings

Outperforms existing neural solvers on synthetic and benchmark VRP instances.

Capable of handling large-scale VRPs up to 18,000 nodes.

Achieves state-of-the-art performance across various VRP contexts.

Abstract

Deep learning has been extensively explored to solve vehicle routing problems (VRPs), which yields a range of data-driven neural solvers with promising outcomes. However, most neural solvers are trained to tackle VRP instances in a relatively monotonous context, e.g., simplifying VRPs by using Euclidean distance between nodes and adhering to a single problem size, which harms their off-the-shelf application in different scenarios. To enhance their versatility, this paper presents a novel lifelong learning framework that incrementally trains a neural solver to manage VRPs in distinct contexts. Specifically, we propose a lifelong learner (LL), exploiting a Transformer network as the backbone, to solve a series of VRPs. The inter-context self-attention mechanism is proposed within LL to transfer the knowledge obtained from solving preceding VRPs into the succeeding ones. On top of that, we develop a dynamic context scheduler (DCS), employing the cross-context experience replay to further facilitate LL looking back on the attained policies of solving preceding VRPs. Extensive results on synthetic and benchmark instances (problem sizes up to 18k) show that our LL is capable of discovering effective policies for tackling generic VRPs in varying contexts, which outperforms other neural solvers and achieves the best performance for most VRPs.