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arXiv 1101.2189math.RTmath.CO
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对合上的$B$ -轨道与Bruhat-Chevalley序的组合学

Combinatorics of $B$-orbits and Bruhat--Chevalley order on involutions

Mikhail V. Ignatyev

摘要:

设$B$是可逆上三角复$n\times n$矩阵群,$\mathfrak{u}$是对角线上有零的上三角复矩阵空间,$\mathfrak{u}^*$是它的对偶空间。$B$基团通过$(g.f)(x)=f(gxg^{-1})$、$g\in B$、$f\in\mathfrak{u}^*$、$x\in\mathfrak{u}$作用于$\mathfrak{u}^*$。对于$S_n$中的每个对合$σ$,$n$字母上的对称群,可以分配$B$ -轨道$Ω_σ\in\mathfrak{u}^*$。我们提出了一个组合描述的轨道闭包诱导的对合集上的偏序。答案是根据车的位置给出的,并且是A的对偶。Melnikov关于$B$的结果-关于$\mathfrak{u}$的轨道。利用F. Incitti,我们还证明了这部分秩序符合限制的Bruhat-Chevalley秩序的集合的对合。

英文摘要:

Let $B$ be the group of invertible upper-triangular complex $n\times n$ matrices, $\mathfrak{u}$ the space of upper-triangular complex matrices with zeroes on the diagonal and $\mathfrak{u}^*$ its dual space. The group $B$ acts on $\mathfrak{u}^*$ by $(g.f)(x)=f(gxg^{-1})$, $g\in B$, $f\in\mathfrak{u}^*$, $x\in\mathfrak{u}$. To each involution $σ$ in $S_n$, the symmetric group on $n$ letters, one can assign the $B$-orbit $Ω_σ\in\mathfrak{u}^*$. We present a combinatorial description of the partial order on the set of involutions induced by the orbit closures. The answer is given in terms of rook placements and is dual to A. Melnikov's results on $B$-orbits on $\mathfrak{u}$. Using results of F. Incitti, we also prove that this partial order coincides with the restriction of the Bruhat--Chevalley order to the set of involutions.

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