Unimodular equivalence of order and chain polytopes

Abstract

Older polytope and chain polytope are two polytopes that arise naturally from a finite partially ordered set. These polytopes have been deeply studied from viewpoints of both combinatorics and commutative algebra. Even though these polytopes possess remarkable combinatorial and algebraic resemblance, they seem to be rarely unimodularly equivalent. In the present paper, we prove the following simple and elegant result: the order polytope and chain polytope for a poset are unimodularly equivalent if and only if that poset avoid the 5-element "X" shape subposet. We also explore a few equivalent statements of the main result.