Testing membership in matroid polyhedra

Abstract

Given a matroid M on E and a nonnegative real vector x=(x_j:j∈E), a fundamental problem is to determine whether x is in the convex hull P of (incidence vectors of) independent sets of M. An algorithm is described for solving this problem for which the amount of computation is bounded by a polynomial in |E|, independently of x, allowing as steps tests of independence in M and additions, subtractions, and comparisons of numbers. In case x ∈ P, the algorithm finds an explicit representation for x which has additional nice properties; in case x ∉ P it finds a most-violated inequality of the system defining P. The same technique is applied to the problem of finding a maximum component-sum vector in the intersection of two matroid polyhedra and a box.