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Linear codes arising from the point-hyperplane geometry -- Part II: the twisted embedding

Combinatorics 2026-04-17 v1 Information Theory math.IT

Abstract

Let Γˉ\bar{\Gamma} be the point-hyperplane geometry of a projective space PG(V),\mathrm{PG(V)}, where VV is a (n+1)(n+1)-dimensional vector space over a finite field Fq\mathbb{F}_q of order q.q. Suppose that σ\sigma is an automorphism of Fq\mathbb{F}_q and consider the projective embedding εσ\varepsilon_{\sigma} of Γˉ\bar{\Gamma} into the projective space PG(VV)\mathrm{PG}(V\otimes V^*) mapping the point ([x],[ξ])Γˉ([x],[\xi])\in \bar{\Gamma} to the projective point represented by the pure tensor xσξx^{\sigma}\otimes \xi, with ξ(x)=0.\xi(x)=0. In [I. Cardinali, L. Giuzzi, Linear codes arising from the point-hyperplane geometry -- part I: the Segre embedding (Jun. 2025). arXiv:2506.21309, doi:10.48550/ARXIV.2506.21309] we focused on the case σ=1\sigma=1 and we studied the projective code arising from the projective system Λ1=ε1(Γˉ).\Lambda_1=\varepsilon_{1}(\bar{\Gamma}). Here we focus on the case σ1\sigma\not=1 and we investigate the linear code C(Λσ){\mathcal C}(\Lambda_{\sigma}) arising from the projective system Λσ=εσ(Γˉ).\Lambda_{\sigma}=\varepsilon_{\sigma}(\bar{\Gamma}). In particular, after having verified that C(Λσ)\mathcal{C}( \Lambda_{\sigma}) is a minimal code, we determine its parameters, its minimum distance as well as its automorphism group. We also give a (geometrical) characterization of its minimum and second lowest weight codewords and determine its maximum weight when qq and nn are both odd.

Keywords

Cite

@article{arxiv.2507.16694,
  title  = {Linear codes arising from the point-hyperplane geometry -- Part II: the twisted embedding},
  author = {Ilaria Cardinali and Luca Giuzzi},
  journal= {arXiv preprint arXiv:2507.16694},
  year   = {2026}
}

Comments

28 pages

R2 v1 2026-07-01T04:13:38.507Z