The permutahedron of N-sparse posets

The permutahedron of a poset is the convex hull of all incidence vectors of linear extensions. For the case of N-sparse posets in which any five elements induce at most one N we give a characterization of the permutahedron in terms of linear inequalities. This yields an LP-solution for minimizing the weighted mean completion time for jobs with unit processing times and N-sparse precedence constraints. We close with an extension of our approach to arbitrary processing times.