Let G=(V,E) be an undirected graph and A⊆V. The authors consider the problem of finding a minimum cost set of edges whose deletion separates every pair of nodes in A. They consider two extended formulations using both node and edge variables. An edge variable formulation has previously been considered for this problem. The authors show that the LP-relaxations of the extended formulations are stronger than the LP-relaxation of the edge variable formulation (even with an extra class of valid inequalities added). This is interesting because, while the LP-relaxations of the extended formulations can be solved in polynomial time, the LP-relaxation of the edge variable formulation cannot. The authors also give a class of valid inequalities for one of the extended formulations. Computational results using the extended formulations are performed.
