Mixed-integer sets from two rows of two adjacent simplex bases
In Andersen et al. (Lecture Notes in Computer Science, vol. 4513, Springer, Berlin, pp. 1-15, 2007) we studied a mixed-integer set arising from two rows of a simplex tableau. We showed that facets of such a set can be obtained from lattice point free triangles and quadrilaterals associated with either three or four variables. In this paper we generalize our findings and show that, when upper bounds on the non-basic variables are also considered, further classes of facets arise that cannot be obtained from triangles and quadrilaterals. Specifically, when exactly one upper bound on a non-basic variable is introduced, stronger inequalities that can be derived from pentagons involving up to six variables also appear.
two rows mixed integer programming valid inequalities lattice-point-free polyhedra