Combined location and routing problems for drug distribution

We present a model for the optimization of logistics operations in emergency health care systems; in particular, we study the problem of efficient distribution of vaccines or drugs through the simultaneous and coordinated use of distribution centers and vehicles. We devise an exact algorithm based on column generation with three different types of columns and branch-and-bound. The pricing subproblems are solved through advanced dynamic programming techniques. In order to strengthen the dual bounds, we adapt two families of cuts from the literature and we introduce a new one. Our framework also includes primal heuristics and ad-hoc branching rules. An experimental campaign on realistic data proves our method to be effective and flexible.