Distributions of weights and a question of Wilf

TL;DR

This paper investigates the distribution of weights in numerical semigroups and related sets, proving convergence results and applying these findings to establish new cases where Wilf's inequality holds.

Contribution

It extends Zhai's asymptotic results on weight distributions to numerical semigroups, demonstrating convergence and deriving new instances satisfying Wilf's inequality.

Findings

Mean weight/maximum weight ratio converges to d/d+1 for certain sets

New classes of numerical semigroups satisfy Wilf's inequality

Application of Zhai's lemma to graded Artinian algebras

Abstract

Let $S$ be a numerical semigroup of embedding dimension $e$ and conductor $c$. The question of Wilf is, if $\#(\mathbb N\setminus S)/c\leq e-1/e$. \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 $x\cdot\gamma$, $x\in\mathbb N^d$, w.\,r. to a positive weight vector $\gamma$: \noindent Let $B\subseteq\mathbb N^d$ be finite and the complement of an $\mathbb N^d$-ideal. Denote by $\operatorname{mean}(B\cdot\gamma)$ the average weight of $B$. Then \[\operatorname{mean}(B\cdot\gamma)/\max(B\cdot\gamma)\leq d/d+1.\] $\bullet$ For the family $\Delta_n:=\{x\in\mathbb N^d|x\cdot\gamma<n+1\}$ of such sets we are able to show, that $\operatorname{mean}(\Delta_n\cdot\gamma)/\max(\Delta_n\cdot\gamma)$ converges to $d/d+1$, as $n$ 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.