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On linear sets of minimum size
Discrete Mathematics ( IF 0.8 ) Pub Date : 2021-03-01 , DOI: 10.1016/j.disc.2020.112230
Dibyayoti Jena , Geertrui Van de Voorde

An $\mathbb{F}_q$-linear set of rank $k$ on a projective line $\mathrm{PG}(1,q^h)$, containing at least one point of weight one, has size at least $q^{k-1}+1$ (see [J. De Beule and G. Van De Voorde, The minimum size of a linear set, J. Comb. Theory, Ser: A 164 (2019), 109-124.]). The classical example of such a set is given by a club. In this paper, we construct a broad family of linear sets meeting this lower bound, where we are able to prescribe the weight of the heaviest point to any value between $k/2$ and $k-1$. Our construction extends the known examples of linear sets of size $q^{k-1}+1$ in $\mathrm{PG}(1,q^h)$ constructed for $k=h=4$ [G. Bonoli and O. Polverino, $\mathbb{F}_q$-Linear blocking sets in $\mathrm{PG}(2,q^4)$, Innov. Incidence Geom. 2 (2005), 35--56.] and $k=h$ in [G. Lunardon and O. Polverino. Blocking sets of size $q^t+q^{t-1}+1$. J. Comb. Theory, Ser: A 90 (2000), 148-158.]. We determine the weight distribution of the constructed linear sets and describe them as the projection of a subgeometry. For small $k$, we investigate whether all linear sets of size $q^{k-1}+1$ arise from our construction. Finally, we modify our construction to define linear sets of size $q^{k-1}+q^{k-2}+\ldots+q^{k-l}+1$ in $\mathrm{PG}(l,q)$. This leads to new infinite families of small minimal blocking sets which are not of Redei type.

中文翻译:

在最小尺寸的线性集上

射影线 $\mathrm{PG}(1,q^h)$ 上的 $\mathbb{F}_q$-秩 $k$ 线性集,包含至少一个权重为 1 的点,大小至少为 $ q^{k-1}+1$(参见 [J. De Beule 和 G. Van De Voorde,线性集的最小大小,J. Comb. Theory, Ser: A 164 (2019), 109-124. ])。俱乐部给出了这种集合的经典示例。在本文中,我们构建了一个满足这个下界的广泛的线性集族,我们能够将最重点的权重规定为 $k/2$ 和 $k-1$ 之间的任何值。我们的构造扩展了在 $\mathrm{PG}(1,q^h)$ 中为 $k=h=4$ [G. Bonoli 和 O. Polverino,$\mathbb{F}_q$-$\mathrm{PG}(2,q^4)$ 中的线性阻塞集,Innov。发生率几何。2 (2005), 35--56.] 和 [G. Lunardon 和 O. Polverino。大小为 $q^t+q^{t-1}+1$ 的阻塞集。J.梳子。理论, Ser: A 90 (2000), 148-158.]。我们确定构建的线性集的权重分布,并将它们描述为子几何的投影。对于小的 $k$,我们调查是否所有大小为 $q^{k-1}+1$ 的线性集都来自我们的构造。最后,我们修改我们的构造以定义 $q^{k-1}+q^{k-2}+\ldots+q^{kl}+1$ 在 $\mathrm{PG}(l, q)$。这导致了非 Redei 类型的小型最小阻塞集的新的无限族。我们修改我们的构造以在 $\mathrm{PG}(l,q) 中定义大小为 $q^{k-1}+q^{k-2}+\ldots+q^{kl}+1$ 的线性集$. 这导致了非 Redei 类型的小型最小阻塞集的新的无限族。我们修改我们的构造以在 $\mathrm{PG}(l,q) 中定义大小为 $q^{k-1}+q^{k-2}+\ldots+q^{kl}+1$ 的线性集$. 这导致了非 Redei 类型的小型最小阻塞集的新的无限族。
更新日期:2021-03-01
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