English

On the gradient of a monomial ideal

Commutative Algebra 2025-11-21 v1 Combinatorics

Abstract

Let KK be a field of characteristic zero, let IS=K[x1,,xn]I \subset S = K[x_1,\dots,x_n] be a homogeneous ideal, and let (I)\partial(I) be its gradient ideal. We study the relationship between regI\mathrm{reg}\,I and reg(I)\mathrm{reg}\,\partial(I). While earlier work by Bus\'e, Dimca, Schenck, and Sticlaru showed these regularities are generally incomparable for hypersurface ideals, we prove they remain incomparable even for monomial ideals with linear resolution, answering a question of J. Herzog. In fact, for any integers aZa \in \mathbb{Z} and b1b \ge - 1, we construct monomial ideals II and JJ such that regIreg(I)=a\mathrm{reg}\,I - \mathrm{reg}\,\partial(I) = a, reg(J)regJ=b\mathrm{reg}\,\partial(J) - \mathrm{reg}\,J = b and JJ has linear resolution. We introduce monomial ideals with differential linear resolution as those monomial ideals whose all iterated gradient ideals have linear resolution. We prove that polymatroidal ideals, equigenerated (strongly) stable ideals, powers of edge ideals with linear resolution, complementary edge ideals with linear resolution, and certain equigenerated squarefree monomial ideals with many generators satisfy this property.

Keywords

Cite

@article{arxiv.2511.15879,
  title  = {On the gradient of a monomial ideal},
  author = {Antonino Ficarra},
  journal= {arXiv preprint arXiv:2511.15879},
  year   = {2025}
}
R2 v1 2026-07-01T07:46:12.936Z