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arXiv 2407.06239math.CO
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格拉斯曼图中一个两点稳定子群的若干轨道

Some orbits of a two-vertex stabilizer in a Grassmann graph

Ian Seong

AI总结:

本文针对有限域上格拉斯曼图$J_q(n,k)$中满足特定距离条件的两点稳定子群,研究其在局部图上的轨道,证明存在5个轨道并求出对应等价划分的结构常数,结合欧几里得表示计算了轨道表示向量的内积与线性依赖。

摘要:

令$\mathbb{F}_q$表示含$q$个元素的有限域,$n,k$为满足$n>2k\geq6$的整数,$V$为$\mathbb{F}_q$上的$n$维向量空间。格拉斯曼图$J_q(n,k)$的顶点集由$V$的所有$k$维子空间构成,当两个顶点的交空间维数为$k-1$时二者相邻,记$\partial$为$J_q(n,k)$的路径长度距离函数。选取$J_q(n,k)$中满足$1<\partial(x,y)<k$的顶点$x,y$,记$\text{Stab}(x,y)$为一般线性群$GL(V)$中同时稳定$x$和$y$的子群。本文研究$\text{Stab}(x,y)$作用在局部图$\Gamma(x)$上的轨道,证明该作用共有5个轨道,且这5个轨道可构造性地给出$\Gamma(x)$的一个等价划分,同时求出了对应的结构常数。为更深入描述这5个轨道,本文引入了与$J_q(n,k)$第二大特征值相关联的$J_q(n,k)$欧几里得表示,每个轨道的特征向量可表示为对应欧氏空间中的向量,本文计算了这5个表示向量涉及的大量内积与线性依赖关系。

英文摘要:

Let $\mathbb{F}_q$ denote a finite field with $q$ elements. Let $n,k$ denote integers with $n>2k\geq 6$. Let $V$ denote a vector space over $\mathbb{F}_{q}$ that has dimension $n$. The vertex set of the Grassmann graph $J_q(n,k)$ consists of the $k$-dimensional subspaces of $V$. Two vertices of $J_q(n,k)$ are adjacent whenever their intersection has dimension $k-1$. Let $\partial$ denote the path-length distance function of $J_q(n,k)$. Pick vertices $x,y$ of $J_q(n,k)$ such that $1<\partial(x,y)<k$. Let $\text{Stab}(x,y)$ denote the subgroup of $GL(V)$ that stabilizes both $x$ and $y$. In this paper, we investigate the orbits of $\text{Stab}(x,y)$ acting on the local graph $Γ(x)$. We show that there are five orbits. By construction, these five orbits give an equitable partition of $Γ(x)$; we find the corresponding structure constants. In order to describe the five orbits more deeply, we bring in a Euclidean representation of $J_q(n,k)$ associated with the second largest eigenvalue of $J_q(n,k)$. By construction, for each orbit its characteristic vector is represented by a vector in the associated Euclidean space. We compute many inner products and linear dependencies involving the five representing vectors.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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