Regularity and h-polynomials of binomial edge ideals
Commutative Algebra
2020-08-27 v2 Combinatorics
Abstract
Let G be a finite simple graph on the vertex set [n]={1,…,n} and K[X,Y]=K[x1,…,xn,y1,…,yn] the polynomial ring in 2n variables over a field K with each degxi=degyj=1. The binomial edge ideal of G is the binomial ideal JG⊂K[X,Y] which is generated by those binomials xiyj−xjyi for which {i,j} is an edge of G. The Hilbert series HK[X,Y]/JG(λ) of K[X,Y]/JG is of the form HK[X,Y]/JG(λ)=hK[X,Y]/JG(λ)/(1−λ)d, where d=dimK[X,Y]/JG and where hK[X,Y]/JG(λ)=h0+h1λ+h2λ2+⋯+hsλs with each hi∈Z and with hs=0 is the h-polynomial of K[X,Y]/JG. It is known that, when K[X,Y]/JG is Cohen-Macaulay, one has reg(K[X,Y]/JG)=deghK[X,Y]/JG(λ), where reg(K[X,Y]/JG) is the (Castelnuovo-Mumford) regularity of K[X,Y]/JG. In the present paper, given arbitrary integers r and s with 2≤r≤s, a finite simple graph G for which reg(K[X,Y]/JG)=r and deghK[X,Y]/JG(λ)=s will be constructed.
Cite
@article{arxiv.1808.06984,
title = {Regularity and h-polynomials of binomial edge ideals},
author = {Takayuki Hibi and Kazunori Matsuda},
journal= {arXiv preprint arXiv:1808.06984},
year = {2020}
}
Comments
6 pages. Conjecture 0.1 has been deleted. A counterexample of Conjecture 0.1 were given in arXiv:1906.05510