English

Hadamard Matrix Torsion

Combinatorics 2021-11-04 v2 Algebraic Topology General Topology

Abstract

We construct a series HMT(n)(n) of 22-dimensional simplicial complexes with torsion H1(H_1(HMT(n))=(Z2)(k1)×(Z4)(k2)××(Z2k)(kk)(n))=(\mathbb{Z}_2)^{{k}\choose{1}} \times (\mathbb{Z}_4)^{{k}\choose{2}} \times \cdots \times (\mathbb{Z}_{2^k})^{{k}\choose{k}}, H1(|H_1(HMT(n))=(n))|=|det(H(n))=nn/2Θ(2nlogn)(n))|=n^{n/2} \in \Theta(2^{n \log n}), where the construction is based on the Hadamard matrices H(n)(n) for n2n\geq 2 a power of 22, i.e., n=2k, k1n=2^k, \ k \geq 1. The examples have linearly many vertices, their face vector is f(HMT(n))=(5n1,3n2+9n6,3n2+4n4)f(HMT(n))=(5n-1,3n^2+9n-6,3n^2+4n-4). Our explicit series with torsion growth in Θ(2nlogn)\Theta(2^{n \log n}) is constructed in quadratic time Θ(n2)\Theta(n^{2}) and improves a previous construction by Speyer with torsion growth in Θ(2n)\Theta(2^{n}), narrowing the gap to the highest possible asymptotic torsion growth in Θ(2n2)\Theta(2^{n^2}) proved by Kalai via a probabilistic argument.

Cite

@article{arxiv.2109.13052,
  title  = {Hadamard Matrix Torsion},
  author = {Davide Lofano and Frank H. Lutz},
  journal= {arXiv preprint arXiv:2109.13052},
  year   = {2021}
}

Comments

16 pages, 5 figures

R2 v1 2026-06-24T06:22:52.500Z