English

Studying the divisibility of power LCM matrics by power GCD matrices on gcd-closed sets

Combinatorics 2025-01-06 v1

Abstract

Let S={x1,,xn}S=\{x_1,\ldots, x_n\} be a gcd-closed set (i.e. (xi,xj)S(x_i,x_j)\in S for all 1i,jn1\le i,j\le n). In 2002, Hong proposed the divisibility problem of characterizing all gcd-closed sets SS with S4|S|\ge 4 such that the GCD matrix (S)(S) divides the LCM matrix [S][S] in the ring Mn(Z)M_{n}(\mathbb{Z}). For xS,x\in S, let GS(x):={zS:z<x,zx and (zyx,yS)y{z,x}}G_S(x):=\{z\in S: z<x, z|x \text{ and } (z|y|x, y\in S)\Rightarrow y\in\{z,x\}\}. In 2009, Feng, Hong and Zhao answered this problem in the context where maxxS{GS(x)}2\max_{x \in S}\{|G_S(x)|\} \leq 2. In 2022, Zhao, Chen and Hong obtained a necessary and sufficient condition on the gcd-closed set SS with maxxS{GS(x)}=3\max_{x \in S}\{|G_S(x)|\}=3 such that (S)[S].(S)|\left[S\right]. Meanwhile, they raised a conjecture on the necessary and sufficient condition such that (S)[S](S)|\left[S\right] holds for the remaining case maxxS{GS(x)}4\max_{x \in S}\{|G_S(x)|\}\ge 4. In this papar, we confirm the Zhao-Chen-Hong conjecture from a novel perspective, consequently solve Hong's open problem completely.

Keywords

Cite

@article{arxiv.2501.01794,
  title  = {Studying the divisibility of power LCM matrics by power GCD matrices on gcd-closed sets},
  author = {Jianrong Zhao and Chenxu Wang and Yu Fu},
  journal= {arXiv preprint arXiv:2501.01794},
  year   = {2025}
}