Complexity of polytope diameters via perfect matchings

The Circuit diameter of polytopes was introduced by Borgwardt, Finhold and Hemmecke [BFH15] as a fundamental tool for the study of circuit augmentation schemes for linear programming and for estimating combinatorial diameters. Determining the complexity of computing the circuit diameter of polytopes was posed as an open problem by Sanità [San20] as well as by Kafer [Kaf22], and was recently reiterated by Borgwardt, Grewe, Kafer, Lee and Sanità [BGKLS24]. In this paper, we solve this problem by showing that computing the circuit diameter of a polytope given in halfspace-description is strongly NP-hard. To prove this result, we show that computing the combinatorial diameter of the perfect matching polytope of a bipartite graph is NP-hard. This complements a result by Sanità (FOCS 2018, [San18]) on the NP-hardness of computing the diameter of fractional matching polytopes and implies the new result that computing the diameter of a 0, 1-polytope is strongly NP-hard, which may be of independent interest. In our second main result, we give a precise graph-theoretic description of the monotone diameter of perfect matching polytopes and use this description to prove that computing the monotone (circuit) diameter of a given input polytope is strongly NP-hard as well.