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0/1-Polytopes related to Latin squares autotopisms

Published 5 May 2011 in math.CO | (1105.1099v1)

Abstract: The set LS(n) of Latin squares of order nn can be represented in R<sup>n<sup>3\mathbb{R}<sup>{n<sup>3} as a (n−1)<sup>3(n-1)<sup>3-dimensional 0/1-polytope. Given an autotopism Θ=(α,β,γ)∈A<em>n\Theta=(\alpha,\beta,\gamma)\in\mathfrak{A}<em>n, we study in this paper the 0/1-polytope related to the subset of LS(n) having Θ\Theta in their autotopism group. Specifically, we prove that this polyhedral structure is generated by a polytope in R<sup>((n</sup></em>α−l<em>α<sup>1)⋅</sup>n<sup>2</sup>+l</em>α<sup>1⋅</sup>n<em>β⋅n)−(l</em>α<sup>1⋅</sup>l<em>β<sup>1⋅</sup>(n−l</em>γ<sup>1)</sup>+l<em>α<sup>1⋅</sup>l</em>γ<sup>1⋅</sup>(n<em>β−l</em>β<sup>1)</sup>+l<em>β<sup>1⋅</sup>l</em>γ<sup>1⋅</sup>(n<em>α−l</em>α<sup>1))\mathbb{R}<sup>{((\mathbf{n}</sup></em>{\alpha}-\mathbf{l}<em>{\alpha}<sup>1)\cdot</sup> n<sup>2</sup> + \mathbf{l}</em>{\alpha}<sup>1\cdot</sup> \mathbf{n}<em>{\beta}\cdot n)-(\mathbf{l}</em>{\alpha}<sup>1\cdot</sup> \mathbf{l}<em>{\beta}<sup>1\cdot</sup> (n -\mathbf{l}</em>{\gamma}<sup>1)</sup> + \mathbf{l}<em>{\alpha}<sup>1\cdot</sup> \mathbf{l}</em>{\gamma}<sup>1\cdot</sup> (\mathbf{n}<em>{\beta} -\mathbf{l}</em>{\beta}<sup>1)</sup> + \mathbf{l}<em>{\beta}<sup>1\cdot</sup> \mathbf{l}</em>{\gamma}<sup>1\cdot</sup> (\mathbf{n}<em>{\alpha} -\mathbf{l}</em>{\alpha}<sup>1))}, where n<em>α\mathbf{n}<em>{\alpha} and n</em>β\mathbf{n}</em>{\beta} are the number of cycles of α\alpha and β\beta, respectively, and lδ<sup>1\mathbf{l}_{\delta}<sup>1 is the number of fixed points of δ\delta, for all δ∈α,β,γ\delta\in {\alpha,\beta,\gamma}. Moreover, we study the dimension of these two polytopes for Latin squares of order up to 9.

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