On the complexity of the separation problem for rounded capacity inequalities

•NP-Completeness of the separation problem of the Rounded Capacity inequalities.•Variants of Subset Sum and Equicut Problems.•Polynomial reductions of the separation problem of Rounded Capacity inequalities.•Answer an open question.

In this paper, we are interested in the separation problem for the so-called rounded capacity inequalities which are valid for the CVRP (Capacitated Vehicle Routing Problem) polytope. Rounded capacity inequalities, as well as the associated separation problem, are of particular interest for solving the CVRP, especially when dealing with the two-index formulation of the CVRP and Branch-and-Cut algorithms based on this formulation. To the best of our knowledge, it is not known in the literature whether this separation problem is NP-hard or polynomial (see for instance Augerat et al. (1998) and Letchford and Salazar (2015)), and it has been conjectured that the problem is NP-hard. In this paper, we prove this conjecture. We also show that the separation problem for rounded capacity inequalities is strongly NP-hard when the considered solution belongs to a particular relaxation of the problem and the clients have all the same demand.