English

The minimum distance of sets of points and the minimum socle degree

Commutative Algebra 2012-03-12 v1

Abstract

Let K\mathbb K be a field of characteristic 0. Let ΓPKn\Gamma\subset\mathbb P^n_{\mathbb K} be a reduced finite set of points, not all contained in a hyperplane. Let hyp(Γ)hyp(\Gamma) be the maximum number of points of Γ\Gamma contained in any hyperplane, and let d(Γ)=Γhyp(Γ)d(\Gamma)=|\Gamma|-hyp(\Gamma). If IR=K[x0,...,xn]I\subset R=\mathbb K[x_0,...,x_n] is the ideal of Γ\Gamma, then in \cite{t1} it is shown that for n=2,3n=2,3, d(Γ)d(\Gamma) has a lower bound expressed in terms of some shift in the graded minimal free resolution of R/IR/I. In these notes we show that this behavior is true in general, for any n2n\geq 2: d(Γ)And(\Gamma)\geq A_n, where An=min{ain}A_n=\min\{a_i-n\} and iR(ai)\oplus_i R(-a_i) is the last module in the graded minimal free resolution of R/IR/I. In the end we also prove that this bound is sharp for a whole class of examples due to Juan Migliore (\cite{m}).

Keywords

Cite

@article{arxiv.1203.2040,
  title  = {The minimum distance of sets of points and the minimum socle degree},
  author = {Stefan O. Tohaneanu},
  journal= {arXiv preprint arXiv:1203.2040},
  year   = {2012}
}

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11 pages