The Symmetric Traveling Salesman Polytope: New Facets from the Graphical Relaxation

The path, the wheelbarrow, and the bicycle inequalities have been shown by Cornuéjols, Fonlupt, and Naddef to be facet-defining for the graphical relaxation of STSP(n), the polytope of the symmetric traveling salesman problem on an n-node complete graph. We show that these inequalities, and some generalizations of them, define facets also for STSP(n). In conclusion, we characterize a large family of facet-defining inequalities for STSP(n) that include, as special cases, most of the inequalities currently known to have this property as the comb, the clique tree, and the chain inequalities. Most of the results given here come from a strong relationship of STSP(n) with its graphical relaxation that we have pointed out in another paper, where the basic proof techniques are also described.