"Poincare Series of Coxeter Groups"의 두 판 사이의 차이

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==introduction==
 
==introduction==
* Poincaré Series of a Coxeter Group $W$ (Poincare series for ring of coinvariants)
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* {{수학노트|url=콕세터_군의_푸앵카레_급수}}
$$
 
P_{W}(q)=\sum_{w\in W}q^{\ell(w)}
 
$$
 
* for finite $W$,
 
$$
 
P_{W}(q)=\prod_{\alpha>0}\frac{q^{\operatorname{ht}(\alpha)+1}-1}{q^{\operatorname{ht}(\alpha)}-1}=\prod_{i=1}^{k}\begin{bmatrix} d_i \end{bmatrix}_{q}
 
$$
 
where $d_i$'s are degrees 
 
http://mathoverflow.net/questions/28422/does-the-poincare-series-of-a-coxeter-group-always-describe-a-flag-variety?rq=1
 
==example==
 
* $A_2$ example
 
* degree : 2,3
 
* $W$ has 6 elements : $1,s_1,s_2,s_1s_2,s_2s_1,s_1s_2s_1$
 
* $P_{W}(q)=1 + 2 q + 2 q^2 + q^3=(1 + q) (1 + q + q^2)$
 
* using heights of roots
 
$$
 
\prod_{\alpha>0}\frac{q^{\operatorname{ht}(\alpha)+1}-1}{q^{\operatorname{ht}(\alpha)}-1}=\frac{q^2-1}{q-1}\frac{q^2-1}{q-1}\frac{q^3-1}{q^2-1}=(1 + q) (1 + q + q^2)
 
$$
 
* using degrees
 
$$
 
\prod_{i=1}^{k}\begin{bmatrix} d_i \end{bmatrix}_{q}=\begin{bmatrix} 2 \end{bmatrix}_{q}\begin{bmatrix} 3 \end{bmatrix}_{q}=(1+q)(1+q+q^2)
 
$$
 
 
 
  
  
 
==related items==
 
==related items==
 
* [[Macdonald constant term conjecture]]
 
* [[Macdonald constant term conjecture]]
* [[Degrees and exponents]]
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[[분류:migrate]]
 
 
 
 
==computational resource==
 
* https://docs.google.com/file/d/0B8XXo8Tve1cxbF9YQmxvNjBFYzQ/edit
 
 
 
 
 
==books==
 
* Richard Kane
 
** 144p, 219p, 236p
 
 
 
 
 
==articles==
 
* Macdonald, I. G. 1972. “The Poincaré Series of a Coxeter Group.” Mathematische Annalen 199 (3) (September 1): 161–174.
 
doi:[http://dx.doi.org/10.1007/BF01431421 10.1007/BF01431421]
 

2020년 11월 12일 (목) 23:24 기준 최신판