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0/1-Polytopes related to Latin squares autotopisms

Combinatorics 2011-05-06 v1

Abstract

The set LS(n) of Latin squares of order nn can be represented in Rn3\mathbb{R}^{n^3} as a (n1)3(n-1)^3-dimensional 0/1-polytope. Given an autotopism Θ=(α,β,γ)An\Theta=(\alpha,\beta,\gamma)\in\mathfrak{A}_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((nαlα1)n2+lα1nβn)(lα1lβ1(nlγ1)+lα1lγ1(nβlβ1)+lβ1lγ1(nαlα1))\mathbb{R}^{((\mathbf{n}_{\alpha}-\mathbf{l}_{\alpha}^1)\cdot n^2 + \mathbf{l}_{\alpha}^1\cdot \mathbf{n}_{\beta}\cdot n)-(\mathbf{l}_{\alpha}^1\cdot \mathbf{l}_{\beta}^1\cdot (n -\mathbf{l}_{\gamma}^1) + \mathbf{l}_{\alpha}^1\cdot \mathbf{l}_{\gamma}^1\cdot (\mathbf{n}_{\beta} -\mathbf{l}_{\beta}^1) + \mathbf{l}_{\beta}^1\cdot \mathbf{l}_{\gamma}^1\cdot (\mathbf{n}_{\alpha} -\mathbf{l}_{\alpha}^1))}, where nα\mathbf{n}_{\alpha} and nβ\mathbf{n}_{\beta} are the number of cycles of α\alpha and β\beta, respectively, and lδ1\mathbf{l}_{\delta}^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.

Keywords

Cite

@article{arxiv.1105.1099,
  title  = {0/1-Polytopes related to Latin squares autotopisms},
  author = {R. M. Falcón},
  journal= {arXiv preprint arXiv:1105.1099},
  year   = {2011}
}

Comments

8 pages, 2 tables