new mathematical model for multiple allocation tree- of-hubs location problem
Betul Kayisoglu, I ̇brahim Akgün

Hub location problems are concerned with determining the locations of hubs and the assignment of service routes between origin-destination (OD) points. Classical hub location problems assume that all hubs are fully interconnected by the hub arcs, i.e., hub-level network is com- plete. However, full interconnection between hub points may not be appropriate in some problems especially when hub arcs have consid- erably high setup costs. In this study, we address the Tree-of-Hubs Location Problem where the complete hub-level network structure is relaxed and the hubs are allowed to be connected to each other in a tree structure. We develop a new mathematical model and an effective heuristic for the problem and present computational results. Unlike most models in the literature that use a complete-network structure with distances satisfying the triangle inequality as an input, the pro- posed model can work directly with physical real-world network data structure (e.g., non-complete road and rail networks) as well as com- plete networks whose costs may or may not satisfy the triangle inequal- ity. That is, the model do not require any specific cost and network structure. The proposed model assume that a non-hub node may get service from one or more hubs, i.e., multiple allocation. This research was supported by the Scientific and Technological Research Council of Turkey (TÜBiTAK Grant No: 114M363).