Conjecture on maximal vertex numbers of maxout polytopes

A (d,n,m)(d,n,m)-maxout polytope is a polytope specified by the parameters dd, nn, and mm, and f0(P)f_0(P) denotes the number of vertices of a polytope PP. Maxout polytopes vertex-number conjecture.

  1. The maximal number of vertices of a (3,n,1)(3,n,1)-maxout polytope equals
4k=02(n1k)4\sum_{k=0}^{2}\binom{n-1}{k}

if nn is odd, and equals

4k=02(n1k)(n2)4\sum_{k=0}^{2}\binom{n-1}{k}-(n-2)

if nn is even.

  1. For 4dn4\leq d\leq n, the maximal number of vertices of a (d,n,1)(d,n,1)-maxout polytope equals
4k=0d1(n1k).4\sum_{k=0}^{d-1}\binom{n-1}{k}.
  1. For 2dn2\leq d\leq n, the maximal number of vertices of a (d,n,m)(d,n,m)-maxout polytope equals
2k=0d1(m1k)max{f0(P)2k=0d1(n1k):P is a (d,n,1)-maxout polytope}.2\sum_{k=0}^{d-1}\binom{m-1}{k}\cdot\max\left\{f_0(P)-2\sum_{k=0}^{d-1}\binom{n-1}{k}:P\text{ is a }(d,n,1)\text{-maxout polytope}\right\}.

These claims arise from computational bounds and examples for three-dimensional zonoboxtopes. The source provides no resolution evidence, so the conjecture remains open.

Sources & referencesView supporting material

Primary source

Andrei Balakin, Shelby Cox, Georg Loho and Bernd Sturmfels, “Maxout Polytopes”, arXiv:2509.21286 (2025).

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