English

On a graph isomorphic to $NO^{+}(6,2)$

Combinatorics 2023-11-17 v3

Abstract

Let Q+(2n1,2)Q^{+}(2n-1,2) be a non-degenerate hyperbolic quadric of PG(2n1,2)PG(2n-1,2). Let NO+(2n,2)NO^{+}(2n,2) be the tangent graph, whose vertices are the points of PG(2n1,2)Q+(2n1,2)PG(2n-1,2) \setminus Q^{+}(2n-1,2) and two vertices u, vu,~v are adjacent if the line joining uu and vv is tangent to Q+(2n1,2)Q^{+}(2n-1,2). Then NO+(2n1,q)NO^{+}(2n-1,q) is a strongly regular graph. Let V24\mathcal{V}^{4}_{2} be the \textit{Veronese surface} in PG(5,q)PG(5,q), and M43\mathcal{M}^{3}_{4} its \textit{secant variety}. When q=2q=2, Q+(5,2)=M43=35|Q^{+}(5,2)|=|\mathcal{M}^{3}_{4}|=35. In this paper we define the graph NM43N\mathcal{M}^{3}_{4}, with 28 vertices in PG(5,2)M43PG(5,2)\setminus\mathcal{M}^{3}_{4} and with the analogue incidence rule of the tangent graph. Such graph is isomorphic to NO+(6,2)NO^{+}(6,2).

Keywords

Cite

@article{arxiv.2211.01057,
  title  = {On a graph isomorphic to $NO^{+}(6,2)$},
  author = {Federico Romaniello and Valentino Smaldore},
  journal= {arXiv preprint arXiv:2211.01057},
  year   = {2023}
}

Comments

10 pages

R2 v1 2026-06-28T05:00:26.409Z