Combinatorial Theory

The polyhedron of unit flows on a directed acyclic graph (DAG) with one source and one sink is known to admit regular unimodular triangulations induced by framings of the DAG. The dual graph of any of these triangulations may be given the structure of the Hasse diagram of a lattice, generalizing many variations of the Tamari lattice and the weak order. We extend this theory to flow polytopes of DAGs which may have multiple sources, multiple sinks, and nontrivial netflow vectors under certain planarity conditions. We construct a unimodular triangulation of such a flow polytope indexed by combinatorial data and give a poset structure on its maximal simplices generalizing the strongly planar one-source-one-sink case.

Mathematics Subject Classifications: 05C21, 05E45, 52B11

Keywords: Framing triangulations, flow polytopes