A Fair OR-ML Framework for Resource Substitution in Large-Scale Networks
Ved Mohan, El Mehdi Er Raqabi, Pascal Van Hentenryck
TL;DR
The paper addresses resource substitution in large-scale logistics networks under fairness constraints, a problem that is NP-hard and difficult to coordinate across decentralized schedulers. It proposes FAIR-SUB, a hybrid OR–ML framework that explicitly models fairness and learns scheduler preferences to guide exploration, producing a portfolio of high-quality, fair substitution options. Key contributions include the explicit fairness formulations (minimax and potential Gini variants), the dynamic per-arc search-space reduction via arc betweenness-based $top_{\kappa_a}$, and strong empirical validation on a large package-delivery network showing substantial gains in computational efficiency while preserving optimality. Practically, this framework enables centralized policy design with decentralized execution, improving service reliability and reducing empty movements in complex logistics networks.
Abstract
Ensuring that the right resource is available at the right location and time remains a major challenge for organizations operating large-scale logistics networks. The challenge comes from uneven demand patterns and the resulting asymmetric flow of resources across the arcs, which create persistent imbalances at the network nodes. Resource substitution among multiple, potentially composite and interchangeable, resource types is a cost-effective way to mitigate these imbalances. This leads to the resource substitution problem, which aims at determining the minimum number of resource substitutions from an initial assignment to minimize the overall network imbalance. In decentralized settings, achieving globally coordinated solutions becomes even more difficult. When substitution entails costs, effective prescriptions must also incorporate fairness and account for the individual preferences of schedulers. This paper presents a generic framework that combines operations research (OR) and machine learning (ML) to enable fair resource substitution in large networks. The OR component models and solves the resource substitution problem under a fairness lens. The ML component leverages historical data to learn schedulers' preferences, guide intelligent exploration of the decision space, and enhance computational efficiency by dynamically selecting the top-$κ$ resources for each arc in the network. The framework produces a portfolio of high-quality solutions from which schedulers can select satisfactory trade-offs. The proposed framework is applied to the network of one of the largest package delivery companies in the world, which serves as the primary motivation for this research. Computational results demonstrate substantial improvements over state-of-the-art methods, including an 80% reduction in model size and a 90% decrease in execution time while preserving optimality.