English

Defect of an octahedron in a rational lattice

Number Theory 2020-01-08 v1 Metric Geometry

Abstract

Consider an arbitrary nn-dimensional lattice Λ\Lambda such that ZnΛQn\mathbb{Z}^n \subset \Lambda \subset \mathbb{Q}^n. Such lattices are called {\it rational} and can always be obtained by adding mnm \le n rational vectors to Zn\mathbb{Z}^n. {\it Defect } d(E,Λ)d({\cal E},\Lambda) of the standard basis E {\cal E} of Zn{\mathbb Z}^n (nn unit vectors going in the directions of the coordinate axes) is defined as the smallest integer dd such that certain (nd) (n-d) vectors from E {\cal E} together with some dd vectors from the lattice Λ\Lambda form a basis of Λ\Lambda. Let ...||...|| be L1L^1-norm on Qn\mathbb{Q}^n. Suppose that for each non-integer xΛx \in \Lambda inequality x>1||x|| > 1 holds. Then the unit octahedron On={xRn:x1}O^n = \left\{{ x} \in \mathbb{R}^n: ||x|| \leqslant 1\right\} is called admissible with respect to Λ\Lambda and d(E,Λ)d({\cal E},\Lambda) is also called defect of the octahedron OnO^n with respect to E\cal{E} and is denoted as d(OEn,Λ)d(O^n_{{\cal E}}, \Lambda). Let dnm=maxΛAmd(OEn,Λ), d_n^m = \max_{\Lambda \in {\cal A}_m} d(O^n_{{\cal E}},\Lambda), where Am {\cal A}_m is the set of all {\it rational} lattices that can be obtained by adding mm rational vectors to Zn\mathbb{Z}^n: Λ=Zn,a1,,amZ,a1,,amQn. \Lambda = \left \langle {\mathbb Z}^n, { a}_1, \dots, { a}_m \right \rangle_{{\mathbb Z}}, { a}_1, \dots, { a}_m \in {\mathbb Q}^n. In this article we show that there exists an absolute positive constant C C such that for any m<nm < n dnmCnln(m+1)lnnm(lnln(nm)m)2 d_n^m \leq C \frac{n \ln (m+1)}{\ln \frac{n}{m}} \left(\ln\ln \left(\frac{n}{m}\right)^m \right)^2 This bound was also claimed in [1],[2][1],[2], however the proof was incorrect. In this article along with giving correct proof we highlight substantial inaccuracies in those articles.

Keywords

Cite

@article{arxiv.1804.08129,
  title  = {Defect of an octahedron in a rational lattice},
  author = {Mikhail Fadin},
  journal= {arXiv preprint arXiv:1804.08129},
  year   = {2020}
}