Weighted Triangle-free 2-matching Problem with Edge-disjoint Forbidden Triangles

The weighted T -free 2-matching problem is the following problem: given an undirected graph G , a weight function on its edge set, and a set T of triangles in G , find a maximum weight 2-matching containing no triangle in T . When T is the set of all triangles in G , this problem is known as the weighted triangle-free 2-matching problem, which is a long-standing open problem. A main contribution of this paper is to give the first polynomial-time algorithm for the weighted T -free 2-matching problem under the assumption that T is a set of edge-disjoint triangles. In our algorithm, a key ingredient is to give an extended formulation representing the solution set, that is, we introduce new variables and represent the convex hull of the feasible solutions as a projection of another polytope in a higher dimensional space. Although our extended formulation has exponentially many inequalities, we show that the separation problem can be solved in polynomial time, which leads to a polynomial-time algorithm for the weighted T -free 2-matching problem.