将车辆路径问题重新定义为边删除距离最大化,揭示最优解的稀疏性与构造偏差。
Graph Edit Distance Formulation for the Vehicle Routing Problem: Theory and Analysis
- 用边删除代价模型重写车辆路径问题,以选边代替排路线
- 最优解仅用5.5%可用边,且3.0%关键边常被启发式算法遗漏
- 提供可解释的边级监督信号,适合图神经网络研究
我们证明车辆路径问题(VRP)可重新表述为图编辑距离(GED)最大化问题。在简单的边删除代价模型下,最小化总路径成本等价于从完全图中删除边的总权重最大化。该形式在边层面建模VRP,解由选择的边构成而非路径序列,支持难以在传统框架中实现的结构性分析:每条边对解质量的贡献归因、最优性差距分解、解的稀疏性表征,以及贪心构造中难以触及的边识别。理论上,我们建立了合并-分解定理,表明Clarke-Wright节省值等于每次合并的GED增量;并提出近似传递定理,将GED近似比转化为VRP成本界。基于此,我们分析了90个具有已知最优解的CVRP基准实例。结果发现:最优路由图仅使用5.5%的可用边;约3.0%的最优边在多次重启的Clarke-Wright启发式中始终未被找到;成本差距可分解为未捕获的最优边与替代的非最优边,二者总权重相当。边加性目标为未来图神经网络的边预测提供了自然的逐边监督信号,其潜在关联留待后续研究。
原文摘要 · Abstract (English)
We show that the Vehicle Routing Problem (VRP) can be reformulated as a Graph Edit Distance (GED) maximization problem. Under a simple edge-deletion cost model, minimizing total route cost is equivalent to maximizing the total weight of edges deleted from the complete instance graph. This formulation models VRP at the edge level, where solutions are defined by selected edges rather than route sequences, enabling structural analyses that are difficult in classical formulations: per-edge attribution of solution quality, decomposition of the optimality gap, characterization of solution sparsity, and identification of edges that are hard to reach by greedy construction. Theoretically, we establish a merge-decomposition theorem showing that Clarke-Wright savings equal per-merge GED increments, and an approximation-transfer theorem that turns GED approximation ratios into VRP cost bounds. Using this reformulation, we analyze 90 CVRP benchmark instances with known optimal solutions. We find that optimal routing graphs use only 5.5% of available edges, that approximately 3.0% of optimal edges are consistently not found by Clarke-Wright heuristics under repeated restarts, and that the cost gap decomposes into missed optimal edges and substituted non-optimal edges of comparable total weight. The edge-additive objective provides a natural per-edge supervision signal for future graph neural network approaches to edge prediction, suggesting a potential connection to graph neural network approaches that we leave for follow-up work.
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