Distributive lattices, polyhedra, and generalized flows

• Published in: European journal of combinatorics Vol. 32; no. 1; pp. 45 - 59
• Main Authors: Felsner, Stefan, Knauer, Kolja
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 2011
• Subjects: Combinatorial analysis; Dominance; Gain; Graph theory; Graphs; Lattices; Mathematical models; Polyhedrons
• ISSN: 0195-6698; 1095-9971
• DOI: 10.1016/j.ejc.2010.07.011

A D -polyhedron is a polyhedron P such that if x , y are in P then so are their componentwise maximums and minimums. In other words, the point set of a D -polyhedron forms a distributive lattice with the dominance order. We provide a full characterization of the bounding hyperplanes of D -polyhedra. Aside from being a nice combination of geometric and order theoretic concepts, D -polyhedra are a unifying generalization of several distributive lattices which arise from graphs. In fact with a D -polyhedron we associate a directed graph with arc-parameters, such that points in the polyhedron correspond to vertex potentials on the graph. Alternatively, an edge-based description of the points of a D -polyhedron can be given. In this model the points correspond to the duals of generalized flows, i.e., duals of flows with gains and losses. These models can be specialized to yield distributive lattices that have been previously studied. Particular specializations are: flows of planar digraphs (Khuller, Naor and Klein), α -orientations of planar graphs (Felsner), c -orientations (Propp) and Δ -bonds of digraphs (Felsner and Knauer). As an additional application we identify a distributive lattice structure on generalized flow of breakeven planar digraphs.