The winding-number conjecture for dilated simplex Ehrhart h*-vectors

Let Δrn={x[0,r]n:xi=r}\Delta_r^n=\{x\in[0,r]^n:\sum x_i=r\} be the (n1)(n-1)-dimensional simplex, and call a decorated ordered set partition ((L1)l1,,(Lk)lk)((L_1)_{l_1},\ldots,(L_k)_{l_k}) simplicial when 1lir11\le l_i\le r-1 and ili=r\sum_i l_i=r. For a simplicial ordered set partition with 1L11\in L_1, let wPw_P denote its winding number. Denote by m0,m1,m_0,m_1,\ldots the numbers of such partitions having winding numbers wP=0,1,2,w_P=0,1,2,\ldots. The dilated-simplex winding-number conjecture. The vector (m0,m1,)(m_0,m_1,\ldots) equals the Ehrhart hh^*-vector of Δrn\Delta_r^n, and is obtained from the generating series

s=0(n1+rsn1)xs.\sum_{s=0}^{\infty}\binom{n-1+rs}{n-1}x^s.

The conjecture proposes a combinatorial interpretation of the Ehrhart hh^*-vector, extending the computationally observed winding-number enumeration for dilated simplices.

Sources & referencesView supporting material

Primary source

Nick Early, “Conjectures for Ehrhart h^*-vectors of Hypersimplices and Dilated Simplices”, arXiv:1710.09507 (2017).

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