English

Distributions of weights and a question of Wilf

Commutative Algebra 2018-04-19 v2

Abstract

Let SS be a numerical semigroup of embedding dimension ee and conductor cc. The question of Wilf is, if #(NS)/ce1/e\#(\mathbb N\setminus S)/c\leq e-1/e. \noindent In (An asymptotic result concerning a question of Wilf, arXiv:1111.2779v1 [math.CO], 2011, Lemma 3), Zhai has shown an analogous inequality for the distribution of weights xγx\cdot\gamma, xNdx\in\mathbb N^d, w.\,r. to a positive weight vector γ\gamma: \noindent Let BNdB\subseteq\mathbb N^d be finite and the complement of an Nd\mathbb N^d-ideal. Denote by mean(Bγ)\operatorname{mean}(B\cdot\gamma) the average weight of BB. Then mean(Bγ)/max(Bγ)d/d+1.\operatorname{mean}(B\cdot\gamma)/\max(B\cdot\gamma)\leq d/d+1. \bullet For the family Δn:={xNdxγ<n+1}\Delta_n:=\{x\in\mathbb N^d|x\cdot\gamma<n+1\} of such sets we are able to show, that mean(Δnγ)/max(Δnγ)\operatorname{mean}(\Delta_n\cdot\gamma)/\max(\Delta_n\cdot\gamma) converges to d/d+1d/d+1, as nn goes to infinity. \bullet Applying Zhai's Lemma 3 to the Hilbert function of a positively graded Artinian algebra yields a new class of numerical semigroups satisfying Wilf's inequality.

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Cite

@article{arxiv.1804.06146,
  title  = {Distributions of weights and a question of Wilf},
  author = {Michael Hellus and Rolf Waldi},
  journal= {arXiv preprint arXiv:1804.06146},
  year   = {2018}
}

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7 pages