Abstract. We provide a nontrivial upper bound for the nonnegative rank of rank-three matrices, which allows us to prove that 6n 7 linear inequalities suffice to describe a convex n-gon up to a linear projection.
PreliminariesConsider a convex polytope P ⊂ R n . An extension [5,8] of P is a polytope Q ⊂ R d such that P can be obtained from Q as an image under a linear projection from R d to R n . An extended formulation [8,10] of P is a description of Q by linear equations and linear inequalities (together with the projection). The size [8, 10] of the extended formulation is the number of facets of Q. The extension complexity [8, 10] of a polytope P is the smallest size of any extended formulation of P , that is, the minimal possible number of inequalities in the description of Q. The number of facets of Q can sometimes be significantly smaller [5] than that of P , and this phenomenon can be used to reduce the complexity of linear programming problems useful for numerous applications [3,5,10