Bruhat decomposition
imported>Pythagoras0님의 2013년 6월 26일 (수) 13:08 판
introduction
- double Bruhat cells
- Bruhat order
- Weyl group action
- The decomposition of G into strata G^{u,v} is 'good with respect to total positivity.
Bruhat cell
- G=GL_{n}
- B : upper triangular matrices \in G
- B_{_} : lower triangular matrices in G
- W=S_{n} we can think of it as a subgroup of G
- Double cosets \(BwB\) and \(B_{-}wB_{-}\) are called Bruhat cells.
double Bruhat cell (DBC)
- \(G^{u,v} =BuB\cap B_{-}vB_{-}\)
- \(G=\cup_{u,v\in W\times W} G^{u,v}\) (disjoint union)
realization of finite type cluster algebra
- Yang, Shih-Wei, 와/과Andrei Zelevinsky. 2008. “Cluster algebras of finite type via Coxeter elements and principal minors”. 0804.3303 (4월 21). http://arxiv.org/abs/0804.3303.
- \(\mathbb{C}[L^{c,c^{-1}}]\) is a cluster algebra of finite type. It has the same type as Cartan matrix.
type A_{n}
- (i) inite seed is given by x=(x_{[1,1]},\cdots,x_{[1,n]}), y=(y_1,\cdots,y_n), B=B(C)
- (ii) The set of cluster variables is \{x_{[i,j]}|1\leq i\leq j\leq n \}
- (iii) The exchange relations
$$x_{[i,k]}x_{[j,l]} = y_{j-1}y_{j}\cdots y_{k} x_{[i,j-2]}jx_{[i,j-2]}+x_{[i,l]}x_{[j,l]}$$ for $1\leq i\leq j-1\leq k\leq l-1\leq n$
- remark : $x_{[i,j]}$ corresponds to the diagonal between i and j in the triangulation of regular $(n+3)$-gon
example
memo
computational resource
encyclopedia
- http://en.wikipedia.org/wiki/Longest_element_of_a_Coxeter_group
- http://eom.springer.de/b/b017690.htm
expositions
- http://www-math.mit.edu/~gyuri/papers/bru1.pdf
- http://pages.uoregon.edu/dmoseley/talks/
- http://math.ucr.edu/home/baez/week186.html
- http://www.math.harvard.edu/~ryanr/bruhat_row-reduction.pdf
articles
- Yang, Shih-Wei, 와/과Andrei Zelevinsky. 2008. “Cluster algebras of finite type via Coxeter elements and principal minors”. 0804.3303 (4월 21). http://arxiv.org/abs/0804.3303.