English

An Increasing normalized depth function

Commutative Algebra 2024-04-10 v2

Abstract

Let K\mathbb{K} be a field and S=K[x1,,xn]S=\mathbb{K}[x_1,\ldots,x_n] be the polynomial ring in nn variables over K\mathbb{K}. Assume that II is a squarefree monomial ideal of SS. For every integer k1k\geq 1, we denote the kk-th squarefree power of II by I[k]I^{[k]}. The normalized depth function of II is defined as gI(k)=depth(S/I[k])(dk1)g_I(k)={\rm depth}(S/I^{[k]})-(d_k-1), where dkd_k denotes the minimum degree of monomials belonging to I[k]I^{[k]}. Erey, Herzog, Hibi and Saeedi Madani conjectured that for any squarefree monomial ideal II, the function gI(k)g_I(k) is nonincreasing. In this short note, we provide a counterexample for this conjecture. Our example in fact shows that gI(2)gI(1)g_I(2)-g_I(1) can be arbitrarily large.

Keywords

Cite

@article{arxiv.2309.13892,
  title  = {An Increasing normalized depth function},
  author = {S. A. Seyed Fakhari},
  journal= {arXiv preprint arXiv:2309.13892},
  year   = {2024}
}

Comments

To appear in Journal of Commutative Algebra