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arXiv · 2512.23006

On subdivisions of the permutahedron and flags of lattice path matroids

Carolina Benedetti
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Abstract

In this manuscript we study the subdivisions of the permutahedron $Π_n$ into two subpolytopes corresponding to flags of positroids, which are in particular flags of lattice path matroids (LPFMs). A subpolytope $P_{[u,v]}$ of $Π_n$ is a Bruhat Interval Polytope (BIP) if $P_{[u,v]}$ is the convex hull of all the permutations (viewed as points in $\RR^n$) in the interval $[u,v]$ in the Bruhat order of $§_n$. We show that the coarsest subdivisions we obtain into LPFMs are the only subdivisions of $Π_n$ via hyperplane splits, into subpolytopes corresponding to BIPs. More specifically, we describe the hyperplanes whose intersection with $Π_n$ give rise to BIPs. Hence, these subdivisions are polytopes coming from points in the complete nonnegative flag variety.

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Carolina Benedetti. 2025-12-28. On subdivisions of the permutahedron and flags of lattice path matroids. https://arxiv.org/abs/2512.23006

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