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In [[mathematics]], a '''complex reflection group''' is a [[Group (mathematics)|group]] acting on a finite-dimensional complex vector space, that is generated by '''complex reflections''': non-trivial elements that fix a complex [[hyperplane]] in space pointwise. (Complex reflections are sometimes called '''pseudo reflections''' or '''unitary reflections''' or sometimes just reflections.) | |||
==Classification== | |||
Any real reflection group becomes a complex reflection group if we extend the scalars from | |||
'''R''' to '''C'''. In particular all [[Coxeter group]]s or [[Weyl group]]s give examples of complex reflection groups. | |||
Any finite complex reflection group is a product of irreducible complex reflection groups, acting on the sum of the corresponding vector spaces. So it is sufficient to classify the irreducible complex reflection groups. | |||
The finite irreducible complex reflection groups were classified by {{Harvs |txt |first=G. C. |last=Shephard |author1-link=Geoffrey Colin Shephard|first2=J. A. |last2=Todd |author2-link=J. A. Todd |year=1954}}. They found an infinite family ''G''(''m'',''p'',''n'') depending on 3 positive integer parameters (with ''p'' dividing ''m''), and 34 exceptional cases, that they numbered from 4 to 37, | |||
listed below. The group | |||
''G''(''m'',''p'',''n''), of order ''m''<sup>''n''</sup>''n''!/''p'', is the semidirect product of the abelian group | |||
of order ''m''<sup>''n''</sup>/''p'' whose elements are (θ<sup>''a''<sub>1</sub></sup>,θ<sup>''a''<sub>2</sub></sup>, ...,θ<sup>''a''<sub>''n''</sub></sup>), by the symmetric group ''S''<sub>''n''</sub> acting by permutations of the coordinates, where θ is a primitive ''m''th root of unity and Σ''a''<sub>''i''</sub>≡ 0 mod ''p''; it is an index ''p'' subgroup of the [[generalized symmetric group]] <math>S(m,n).</math> | |||
Special cases of ''G''(''m'',''p'',''n''): | |||
*''G''(''1'',''1'',''n'') is the Coxeter group ''A''<sub>''n''−1</sub> | |||
*''G''(''2'',''1'',''n'') is the Coxeter group ''B''<sub>''n''</sub> = ''C''<sub>''n''</sub> | |||
*''G''(''2'',''2'',''n'') is the Coxeter group ''D''<sub>''n''</sub> | |||
*''G''(''m'',''p'',''1'') is a cyclic group of order ''m''/''p''. | |||
*''G''(''m'',''m'',''2'') is the Coxeter group ''I''<sub>''2''</sub>(''m'') (and the Weyl group ''G''<sub>2</sub> when ''m'' = 6). | |||
*The group ''G''(''m'',''p'',''n'') acts irreducibly on '''C'''<sup>''n''</sup> except in the cases ''m''=1, ''n''>1 (symmetric group) and ''G''(2,2,2) (Klein 4 group), when '''C'''<sup>''n''</sup> splits as a sum of irreducible representations of dimensions 1 and ''n''−1. | |||
*The only cases when two groups ''G''(''m'',''p'',''n'') are isomorphic as complex reflection groups are that ''G''(''ma'',''pa'',1) is isomorphic to ''G''(''mb'',''pb'',1) for any positive integers ''a'',''b''. However there are other cases when two such groups are isomorphic as abstract groups. | |||
*The complex reflection group ''G''(2,2,3) is isomorphic as a complex reflection group to ''G''(1,1,4) restricted to a 3 dimensional space. | |||
*The complex reflection group ''G''(3,3,2) is isomorphic as a complex reflection group to ''G''(1,1,3) restricted to a 2 dimensional space. | |||
*The complex reflection group ''G''(2''p'',''p'',1) is isomorphic as a complex reflection group to ''G''(1,1,2) restricted to a 1 dimensional space. | |||
==List of irreducible complex reflection groups== | |||
There are a few duplicates in the first 3 lines of this list; see the previous section for details. | |||
*'''ST''' is the Shephard–Todd number of the reflection group. | |||
*'''Rank''' is the dimension of the complex vector space the group acts on. | |||
*'''Structure''' describes the structure of the group. The symbol * stands for a [[central product]] of two groups. For rank 2, the quotient by the (cyclic) center is the group of rotations of a tetrahedron, octahedron, or icosahedron (''T'' = Alt(4), ''O'' = Sym(4), ''I'' = Alt(5), of orders 12, 24, 60), as stated in the table. For the notation 2<sup>1+4</sup>, see [[extra special group]]. | |||
*'''Order''' is the number of elements of the group. | |||
*'''Reflections''' describes the number of reflections: 2<sup>6</sup>4<sup>12</sup> means that there are 6 reflections of order 2 and 12 of order 4. | |||
*'''Degrees''' gives the degrees of the fundamental invariants of the ring of polynomial invariants. For example, the invariants of group number 4 form a polynomial ring with 2 generators of degrees 4 and 6. | |||
{| class="wikitable" style="margin: 1em auto; text-align: center;" | |||
|- | |||
! ST | |||
! Rank | |||
! Structure and names | |||
! Order | |||
! Reflections | |||
! Degrees | |||
! Codegrees | |||
|- | |||
| 1 | |||
| ''n''−1 | |||
| [[Symmetric group]] ''G''(1,1,''n'') = Sym(''n'') | |||
| ''n''! | |||
| 2<sup>''n''(''n'' − 1)/2</sup> | |||
| 2, 3, ...,''n'' | |||
| 0,1,...,''n'' − 2 | |||
|- | |||
| 2 | |||
| ''n'' | |||
| ''G''(''m'',''p'',''n'') ''m'' > 1, ''n'' > 1, ''p''<nowiki>|</nowiki>''m'' (''G''(2,2,2) is reducible) | |||
| ''m''<sup>''n''</sup>''n''!/''p'' | |||
| 2<sup>''mn''(''n''−1)/2</sup>,''d''<sup>''n''φ(''d'')</sup> (''d''<nowiki>|</nowiki>''m''/''p'', ''d'' > 1) | |||
| ''m'',2''m'',..,(''n'' − 1)''m''; ''mn''/''p'' | |||
| 0,''m'',..., (''n'' − 1)''m'' if ''p'' < ''m''; 0,''m'',...,(''n'' − 2)''m'', (''n'' − 1)''m'' − ''n'' if ''p'' = ''m'' | |||
|- | |||
| 3 | |||
| 1 | |||
| Cyclic group ''G''(''m'',1,1) = '''Z'''<sub>''m''</sub> | |||
| ''m'' | |||
| ''d''<sup>φ(''d'')</sup> (''d''<nowiki>|</nowiki>''m'', ''d'' > 1) | |||
| ''m'' | |||
| 0 | |||
|- | |||
| 4 | |||
| 2 | |||
| '''Z'''<sub>2</sub>.''T'' = 3[3]3 | |||
| 24 | |||
| 3<sup>8</sup> | |||
| 4,6 | |||
| 0,2 | |||
|- | |||
| 5 | |||
| 2 | |||
| '''Z'''<sub>6</sub>.''T'' = 3[4]3 | |||
| 72 | |||
| 3<sup>16</sup> | |||
| 6,12 | |||
| 0,6 | |||
|- | |||
| 6 | |||
| 2 | |||
| '''Z'''<sub>4</sub>.''T'' = 3[6]2 | |||
| 48 | |||
| 2<sup>6</sup>3<sup>8</sup> | |||
| 4,12 | |||
| 0,8 | |||
|- | |||
| 7 | |||
| 2 | |||
| '''Z'''<sub>12</sub>.''T'' = 〈3,3,3〉<sub>2</sub> | |||
| 144 | |||
| 2<sup>6</sup>3<sup>16</sup> | |||
| 12,12 | |||
| 0,12 | |||
|- | |||
| 8 | |||
| 2 | |||
| '''Z'''<sub>4</sub>.''O'' = 4[3]4 | |||
| 96 | |||
| 2<sup>6</sup>4<sup>12</sup> | |||
| 8,12 | |||
| 0,4 | |||
|- | |||
| 9 | |||
| 2 | |||
| '''Z'''<sub>8</sub>.''O'' = 4[6]2 | |||
| 192 | |||
| 2<sup>18</sup>4<sup>12</sup> | |||
| 8,24 | |||
| 0,16 | |||
|- | |||
| 10 | |||
| 2 | |||
| '''Z'''<sub>12</sub>.''O'' = 4[4]3 | |||
| 288 | |||
| 2<sup>6</sup>3<sup>16</sup>4<sup>12</sup> | |||
| 12,24 | |||
| 0,12 | |||
|- | |||
| 11 | |||
| 2 | |||
| '''Z'''<sub>24</sub>.''O'' = 〈4,3,2〉<sub>12</sub> | |||
| 576 | |||
| 2<sup>18</sup>3<sup>16</sup>4<sup>12 | |||
| 24,24 | |||
| 0,24 | |||
|- | |||
| 12 | |||
| 2 | |||
| '''Z'''<sub>2</sub>.''O''= GL<sub>2</sub>('''F'''<sub>3</sub>) | |||
| 48 | |||
| 2<sup>12</sup> | |||
| 6,8 | |||
| 0,10 | |||
|- | |||
| 13 | |||
| 2 | |||
| '''Z'''<sub>4</sub>.''O'' = 〈4,3,2〉<sub>2</sub> | |||
| 96 | |||
| 2<sup>18</sup> | |||
| 8,12 | |||
| 0,16 | |||
|- | |||
| 14 | |||
| 2 | |||
| '''Z'''<sub>6</sub>.''O'' = 3[8]2 | |||
| 144 | |||
| 2<sup>12</sup>3<sup>16</sup> | |||
| 6,24 | |||
| 0,18 | |||
|- | |||
| 15 | |||
| 2 | |||
| '''Z'''<sub>12</sub>.''O'' = 〈4,3,2〉<sub>6</sub> | |||
| 288 | |||
| 2<sup>18</sup>3<sup>16</sup> | |||
| 12,24 | |||
| 0,24 | |||
|- | |||
| 16 | |||
| 2 | |||
| '''Z'''<sub>10</sub>.''I'' = 5[3]5 | |||
| 600 | |||
| 5<sup>48</sup> | |||
| 20,30 | |||
| 0,10 | |||
|- | |||
| 17 | |||
| 2 | |||
| '''Z'''<sub>20</sub>.''I'' = 5[6]2 | |||
| 1200 | |||
| 2<sup>30</sup>5<sup>48</sup> | |||
| 20,60 | |||
| 0,40 | |||
|- | |||
| 18 | |||
| 2 | |||
| '''Z'''<sub>30</sub>.''I'' = 5[4]3 | |||
| 1800 | |||
| 3<sup>40</sup>5<sup>48</sup> | |||
| 30,60 | |||
| 0,30 | |||
|- | |||
| 19 | |||
| 2 | |||
| '''Z'''<sub>60</sub>.''I'' = 〈5,3,2〉<sub>30</sub> | |||
| 3600 | |||
| 2<sup>30</sup>3<sup>40</sup>5<sup>48</sup> | |||
| 60,60 | |||
| 0,60 | |||
|- | |||
| 20 | |||
| 2 | |||
| '''Z'''<sub>6</sub>.''I'' = 3[5]3 | |||
| 360 | |||
| 3<sup>40</sup> | |||
| 12,30 | |||
| 0,18 | |||
|- | |||
| 21 | |||
| 2 | |||
| '''Z'''<sub>12</sub>.''I'' = 3[10]2 | |||
| 720 | |||
| 2<sup>30</sup>3<sup>40</sup> | |||
| 12,60 | |||
| 0,48 | |||
|- | |||
| 22 | |||
| 2 | |||
| '''Z'''<sub>4</sub>.''I'' = 〈5,3,2〉<sub>2</sub> | |||
| 240 | |||
| 2<sup>30</sup> | |||
| 12,20 | |||
| 0,28 | |||
|- | |||
| 23 | |||
| 3 | |||
| W(H<sub>3</sub>) = '''Z'''<sub>2</sub> × PSL<sub>2</sub>(5), Coxeter | |||
| 120 | |||
| 2<sup>15</sup> | |||
| 2,6,10 | |||
| 0,4,8 | |||
|- | |||
| 24 | |||
| 3 | |||
| W(J<sub>3</sub>(4)) = '''Z'''<sub>2</sub> × PSL<sub>2</sub>(7), [[Klein quartic|Klein]] | |||
| 336 | |||
| 2<sup>21</sup> | |||
| 4,6,14 | |||
| 0,8,10 | |||
|- | |||
| 25 | |||
| 3 | |||
| W(L<sub>3</sub>) = W(P<sub>3</sub>) = 3<sup>1+2</sup>.SL<sub>2</sub>(3), [[Hessian group|Hessian]] | |||
| 648 | |||
| 3<sup>24</sup> | |||
| 6,9,12 | |||
| 0,3,6 | |||
|- | |||
| 26 | |||
| 3 | |||
| W(M<sub>3</sub>) ='''Z'''<sub>2</sub> ×3<sup>1+2</sup>.SL<sub>2</sub>(3), [[Hessian group|Hessian]] | |||
| 1296 | |||
| 2<sup>9</sup> 3<sup>24</sup> | |||
| 6,12,18 | |||
| 0,6,12 | |||
|- | |||
| 27 | |||
| 3 | |||
| W(J<sub>3</sub>(5)) = '''Z'''<sub>2</sub> ×('''Z'''<sub>3</sub>.Alt(6)), [[Valentiner group|Valentiner]] | |||
| 2160 | |||
| 2<sup>45</sup> | |||
| 6,12,30 | |||
| 0,18,24 | |||
|- | |||
| 28 | |||
| 4 | |||
| W(F<sub>4</sub>) = (SL<sub>2</sub>(3)* SL<sub>2</sub>(3)).('''Z'''<sub>2</sub> × '''Z'''<sub>2</sub>) Weyl | |||
| 1152 | |||
| 2<sup>12+12</sup> | |||
| 2,6,8,12 | |||
| 0,4,6,10 | |||
|- | |||
| 29 | |||
| 4 | |||
| W(N<sub>4</sub>) = ('''Z'''<sub>4</sub>*2<sup>1 + 4</sup>).Sym(5) | |||
| 7680 | |||
| 2<sup>40</sup> | |||
| 4,8,12,20 | |||
| 0,8,12,16 | |||
|- | |||
| 30 | |||
| 4 | |||
| W(H<sub>4</sub>) = (SL<sub>2</sub>(5)*SL<sub>2</sub>(5)).'''Z'''<sub>2</sub> Coxeter | |||
| 14400 | |||
| 2<sup>60</sup> | |||
| 2, 12, 20,30 | |||
| 0,10,18,28 | |||
|- | |||
| 31 | |||
| 4 | |||
| W(EN<sub>4</sub>) = W(O<sub>4</sub>) = ('''Z'''<sub>4</sub>*2<sup>1 + 4</sup>).Sp<sub>4</sub>(2) | |||
| 46080 | |||
| 2<sup>60</sup> | |||
| 8,12,20,24 | |||
| 0,12,16,28 | |||
|- | |||
| 32 | |||
| 4 | |||
| W(L<sub>4</sub>) = '''Z'''<sub>3</sub> × Sp<sub>4</sub>(3) | |||
| 155520 | |||
| 3<sup>80</sup> | |||
| 12,18,24,30 | |||
| 0,6,12,18 | |||
|- | |||
| 33 | |||
| 5 | |||
| W(K<sub>5</sub>) = '''Z'''<sub>2</sub> ×Ω<sub>5</sub>(3) = '''Z'''<sub>2</sub> × PSp<sub>4</sub>(3) = '''Z'''<sub>2</sub> × PSU<sub>4</sub>(2) | |||
| 51840 | |||
| 2<sup>45</sup> | |||
| 4,6,10,12,18 | |||
| 0,6,8,12,14 | |||
|- | |||
| 34 | |||
| 6 | |||
| W(K<sub>6</sub>)= '''Z'''<sub>3</sub>.Ω{{su|p=−|b=6}}(3).'''Z'''<sub>2</sub>, [[Mitchell's group]] | |||
| 39191040 | |||
| 2<sup>126</sup> | |||
| 6,12,18,24,30,42 | |||
| 0,12,18,24,30,36 | |||
|- | |||
| 35 | |||
| 6 | |||
| W(E<sub>6</sub>) = SO<sub>5</sub>(3) = O{{su|p=−|b=6}}</sub>(2) = PSp<sub>4</sub>(3).'''Z'''<sub>2</sub> = PSU<sub>4</sub>(2).'''Z'''<sub>2</sub>, Weyl | |||
| 51840 | |||
| 2<sup>36</sup> | |||
| 2,5,6,8,9,12 | |||
| 0,3,4,6,7,10 | |||
|- | |||
| 36 | |||
| 7 | |||
| W(E<sub>7</sub>) = '''Z'''<sub>2</sub> ×Sp<sub>6</sub>(2), Weyl | |||
| 2903040 | |||
| 2<sup>63</sup> | |||
| 2,6,8,10,12,14,18 | |||
| 0,4,6,8,10,12,16 | |||
|- | |||
| 37 | |||
| 8 | |||
| W(E<sub>8</sub>)= '''Z'''<sub>2</sub>.O{{su|p=+|b=8}}(2), Weyl | |||
| 696729600 | |||
| 2<sup>120</sup> | |||
| 2,8,12,14,18,20,24,30 | |||
| 0,6,10,12,16,18,22,28 | |||
|} | |||
For more information, including diagrams, presentations, and codegrees of complex reflection groups, see the tables in {{harvs | last1=Broué | first1=Michel | last2=Malle | first2=Gunter | last3=Rouquier | first3=Raphaël | title=Complex reflection groups, braid groups, Hecke algebras | url=http://citeseer.ist.psu.edu/cache/papers/cs/14118/http:zSzzSzwww.math.jussieu.frzSz~rouquierzSzpreprintszSzbrmaro.pdf/complex-reflection-groups-braid.pdf | mr=1637497 | year=1998 | journal=[[Journal für die reine und angewandte Mathematik]] | issn=0075-4102 | volume=500 | pages=127–190}}. | |||
==Degrees== | |||
Shephard and Todd proved that a finite group acting on a complex vector space is a complex reflection group if and only if its ring of invariants is a polynomial ring ([[Chevalley–Shephard–Todd theorem]]). For <math>\ell</math> being the ''rank'' of the reflection group, the degrees <math>d_1 \leq d_2 \leq \ldots \leq d_\ell</math> of the generators of the ring of invariants are called ''degrees of W'' and are listed in the column above headed "degrees". They also showed that many other invariants of the group are determined by the degrees as follows: | |||
*The center of an irreducible reflection group is cyclic of order equal to the greatest common divisor of the degrees. | |||
*The order of a complex reflection group is the product of its degrees. | |||
*The number of reflections is the sum of the degrees minus the rank. | |||
*An irreducible complex reflection group comes from a real reflection group if and only if it has an invariant of degree 2. | |||
*The degrees ''d''<sub>i</sub> satisfy the formula <math>\prod_{i=1}^\ell(q+d_i-1)= \sum_{w\in W}q^{\dim(V^w)}.</math> | |||
==Codegrees== | |||
For <math>\ell</math> being the ''rank'' of the reflection group, the codegrees <math>d^*_1 \geq d^*_2 \geq \ldots \geq d^*_\ell</math> of W can be defined by | |||
<math>\prod_{i=1}^\ell(q-d^*_i-1)= \sum_{w\in W}\det(w)q^{\dim(V^w)}.</math> | |||
*For a real reflection group, the codegrees are the degrees minus 2. | |||
*The number of reflection hyperplanes is the sum of the codegrees plus the rank. | |||
==Well-generated complex reflection groups== | |||
An irreducible complex reflection group of ''rank'' <math>\ell</math> is generated by <math>\ell</math> or by <math>\ell+1</math> reflections. It is said to be ''well-generated'' if it is generated by <math>\ell</math> reflections ; it is proved that this is equivalent to the property <math>d_i + d^*_i = d_\ell</math> for all <math>1 \leq i \leq \ell</math>. For irreducible well-generated complex reflection groups, the Coxeter number <math>h</math> is defined to be the largest degree, <math>h := d_\ell</math>. A reducible complex reflection group is said to be well-generated if it is a product of irreducible well-generated complex reflection groups. Any finite real reflection group is well-generated. | |||
==References== | |||
*{{Citation | last1=Broué | first1=Michel | last2=Malle | first2=Gunter | last3=Rouquier | first3=Raphaël | authorlink3=Raphaël Rouquier | title=Representations of groups (Banff, AB, 1994) | url=http://www.maths.ox.ac.uk/~rouquier/papers/banff.pdf | publisher=[[American Mathematical Society]] | location=Providence, R.I. | series=CMS Conf. Proc. | mr=1357192 | year=1995 | volume=16 | chapter=On complex reflection groups and their associated braid groups | pages=1–13}} | |||
*{{Citation | last1=Broué | first1=Michel | last2=Malle | first2=Gunter | last3=Rouquier | first3=Raphaël | authorlink3=Raphaël Rouquier | title=Complex reflection groups, braid groups, Hecke algebras | id = {{citeseerx|10.1.1.128.2907}} | mr=1637497 | year=1998 | journal=[[Journal für die reine und angewandte Mathematik]] | issn=0075-4102 | volume=500 | pages=127–190}} | |||
*{{Citation | last1=Deligne | first1=Pierre | author1-link=Pierre Deligne | title=Les immeubles des groupes de tresses généralisés | doi=10.1007/BF01406236 | mr=0422673 | year=1972 | journal=[[Inventiones Mathematicae]] | issn=0020-9910 | volume=17 | pages=273–302 | issue=4}} | |||
*Hiller, Howard ''Geometry of Coxeter groups.'' Research Notes in Mathematics, 54. Pitman (Advanced Publishing Program), Boston, Mass.-London, 1982. iv+213 pp. ISBN 0-273-08517-4* | |||
*{{Citation | last1=Lehrer | first1=Gustav I. | last2=Taylor | first2=Donald E. | title=Unitary reflection groups | publisher=[[Cambridge University Press]] | series=Australian Mathematical Society Lecture Series | isbn=978-0-521-74989-3 | mr=2542964 | year=2009 | volume=20}} | |||
*{{Citation | last1=Shephard | first1=G. C. | last2=Todd | first2=J. A. | title=Finite unitary reflection groups | url=http://books.google.com/?id=Bi7EKLHppuYC | mr=0059914 | year=1954 | journal=Canadian Journal of Mathematics. Journal Canadien de Mathématiques | issn=0008-414X | volume=6 | pages=274–304 | publisher=Canadian Mathematical Society | doi=10.4153/CJM-1954-028-3}} | |||
==External links== | |||
*[http://magma.maths.usyd.edu.au/magma/htmlhelp/text1038.htm ''MAGMA Computational Algebra System'' page] | |||
[[Category:Lie groups]] | |||
[[Category:Geometry]] | |||
[[Category:Group theory]] |
Revision as of 16:57, 15 March 2013
In mathematics, a complex reflection group is a group acting on a finite-dimensional complex vector space, that is generated by complex reflections: non-trivial elements that fix a complex hyperplane in space pointwise. (Complex reflections are sometimes called pseudo reflections or unitary reflections or sometimes just reflections.)
Classification
Any real reflection group becomes a complex reflection group if we extend the scalars from R to C. In particular all Coxeter groups or Weyl groups give examples of complex reflection groups.
Any finite complex reflection group is a product of irreducible complex reflection groups, acting on the sum of the corresponding vector spaces. So it is sufficient to classify the irreducible complex reflection groups.
The finite irreducible complex reflection groups were classified by Template:Harvs. They found an infinite family G(m,p,n) depending on 3 positive integer parameters (with p dividing m), and 34 exceptional cases, that they numbered from 4 to 37, listed below. The group G(m,p,n), of order mnn!/p, is the semidirect product of the abelian group of order mn/p whose elements are (θa1,θa2, ...,θan), by the symmetric group Sn acting by permutations of the coordinates, where θ is a primitive mth root of unity and Σai≡ 0 mod p; it is an index p subgroup of the generalized symmetric group
Special cases of G(m,p,n):
- G(1,1,n) is the Coxeter group An−1
- G(2,1,n) is the Coxeter group Bn = Cn
- G(2,2,n) is the Coxeter group Dn
- G(m,p,1) is a cyclic group of order m/p.
- G(m,m,2) is the Coxeter group I2(m) (and the Weyl group G2 when m = 6).
- The group G(m,p,n) acts irreducibly on Cn except in the cases m=1, n>1 (symmetric group) and G(2,2,2) (Klein 4 group), when Cn splits as a sum of irreducible representations of dimensions 1 and n−1.
- The only cases when two groups G(m,p,n) are isomorphic as complex reflection groups are that G(ma,pa,1) is isomorphic to G(mb,pb,1) for any positive integers a,b. However there are other cases when two such groups are isomorphic as abstract groups.
- The complex reflection group G(2,2,3) is isomorphic as a complex reflection group to G(1,1,4) restricted to a 3 dimensional space.
- The complex reflection group G(3,3,2) is isomorphic as a complex reflection group to G(1,1,3) restricted to a 2 dimensional space.
- The complex reflection group G(2p,p,1) is isomorphic as a complex reflection group to G(1,1,2) restricted to a 1 dimensional space.
List of irreducible complex reflection groups
There are a few duplicates in the first 3 lines of this list; see the previous section for details.
- ST is the Shephard–Todd number of the reflection group.
- Rank is the dimension of the complex vector space the group acts on.
- Structure describes the structure of the group. The symbol * stands for a central product of two groups. For rank 2, the quotient by the (cyclic) center is the group of rotations of a tetrahedron, octahedron, or icosahedron (T = Alt(4), O = Sym(4), I = Alt(5), of orders 12, 24, 60), as stated in the table. For the notation 21+4, see extra special group.
- Order is the number of elements of the group.
- Reflections describes the number of reflections: 26412 means that there are 6 reflections of order 2 and 12 of order 4.
- Degrees gives the degrees of the fundamental invariants of the ring of polynomial invariants. For example, the invariants of group number 4 form a polynomial ring with 2 generators of degrees 4 and 6.
ST | Rank | Structure and names | Order | Reflections | Degrees | Codegrees |
---|---|---|---|---|---|---|
1 | n−1 | Symmetric group G(1,1,n) = Sym(n) | n! | 2n(n − 1)/2 | 2, 3, ...,n | 0,1,...,n − 2 |
2 | n | G(m,p,n) m > 1, n > 1, p|m (G(2,2,2) is reducible) | mnn!/p | 2mn(n−1)/2,dnφ(d) (d|m/p, d > 1) | m,2m,..,(n − 1)m; mn/p | 0,m,..., (n − 1)m if p < m; 0,m,...,(n − 2)m, (n − 1)m − n if p = m |
3 | 1 | Cyclic group G(m,1,1) = Zm | m | dφ(d) (d|m, d > 1) | m | 0 |
4 | 2 | Z2.T = 3[3]3 | 24 | 38 | 4,6 | 0,2 |
5 | 2 | Z6.T = 3[4]3 | 72 | 316 | 6,12 | 0,6 |
6 | 2 | Z4.T = 3[6]2 | 48 | 2638 | 4,12 | 0,8 |
7 | 2 | Z12.T = 〈3,3,3〉2 | 144 | 26316 | 12,12 | 0,12 |
8 | 2 | Z4.O = 4[3]4 | 96 | 26412 | 8,12 | 0,4 |
9 | 2 | Z8.O = 4[6]2 | 192 | 218412 | 8,24 | 0,16 |
10 | 2 | Z12.O = 4[4]3 | 288 | 26316412 | 12,24 | 0,12 |
11 | 2 | Z24.O = 〈4,3,2〉12 | 576 | 218316412 | 24,24 | 0,24 |
12 | 2 | Z2.O= GL2(F3) | 48 | 212 | 6,8 | 0,10 |
13 | 2 | Z4.O = 〈4,3,2〉2 | 96 | 218 | 8,12 | 0,16 |
14 | 2 | Z6.O = 3[8]2 | 144 | 212316 | 6,24 | 0,18 |
15 | 2 | Z12.O = 〈4,3,2〉6 | 288 | 218316 | 12,24 | 0,24 |
16 | 2 | Z10.I = 5[3]5 | 600 | 548 | 20,30 | 0,10 |
17 | 2 | Z20.I = 5[6]2 | 1200 | 230548 | 20,60 | 0,40 |
18 | 2 | Z30.I = 5[4]3 | 1800 | 340548 | 30,60 | 0,30 |
19 | 2 | Z60.I = 〈5,3,2〉30 | 3600 | 230340548 | 60,60 | 0,60 |
20 | 2 | Z6.I = 3[5]3 | 360 | 340 | 12,30 | 0,18 |
21 | 2 | Z12.I = 3[10]2 | 720 | 230340 | 12,60 | 0,48 |
22 | 2 | Z4.I = 〈5,3,2〉2 | 240 | 230 | 12,20 | 0,28 |
23 | 3 | W(H3) = Z2 × PSL2(5), Coxeter | 120 | 215 | 2,6,10 | 0,4,8 |
24 | 3 | W(J3(4)) = Z2 × PSL2(7), Klein | 336 | 221 | 4,6,14 | 0,8,10 |
25 | 3 | W(L3) = W(P3) = 31+2.SL2(3), Hessian | 648 | 324 | 6,9,12 | 0,3,6 |
26 | 3 | W(M3) =Z2 ×31+2.SL2(3), Hessian | 1296 | 29 324 | 6,12,18 | 0,6,12 |
27 | 3 | W(J3(5)) = Z2 ×(Z3.Alt(6)), Valentiner | 2160 | 245 | 6,12,30 | 0,18,24 |
28 | 4 | W(F4) = (SL2(3)* SL2(3)).(Z2 × Z2) Weyl | 1152 | 212+12 | 2,6,8,12 | 0,4,6,10 |
29 | 4 | W(N4) = (Z4*21 + 4).Sym(5) | 7680 | 240 | 4,8,12,20 | 0,8,12,16 |
30 | 4 | W(H4) = (SL2(5)*SL2(5)).Z2 Coxeter | 14400 | 260 | 2, 12, 20,30 | 0,10,18,28 |
31 | 4 | W(EN4) = W(O4) = (Z4*21 + 4).Sp4(2) | 46080 | 260 | 8,12,20,24 | 0,12,16,28 |
32 | 4 | W(L4) = Z3 × Sp4(3) | 155520 | 380 | 12,18,24,30 | 0,6,12,18 |
33 | 5 | W(K5) = Z2 ×Ω5(3) = Z2 × PSp4(3) = Z2 × PSU4(2) | 51840 | 245 | 4,6,10,12,18 | 0,6,8,12,14 |
34 | 6 | W(K6)= Z3.ΩTemplate:Su(3).Z2, Mitchell's group | 39191040 | 2126 | 6,12,18,24,30,42 | 0,12,18,24,30,36 |
35 | 6 | W(E6) = SO5(3) = OTemplate:Su(2) = PSp4(3).Z2 = PSU4(2).Z2, Weyl | 51840 | 236 | 2,5,6,8,9,12 | 0,3,4,6,7,10 |
36 | 7 | W(E7) = Z2 ×Sp6(2), Weyl | 2903040 | 263 | 2,6,8,10,12,14,18 | 0,4,6,8,10,12,16 |
37 | 8 | W(E8)= Z2.OTemplate:Su(2), Weyl | 696729600 | 2120 | 2,8,12,14,18,20,24,30 | 0,6,10,12,16,18,22,28 |
For more information, including diagrams, presentations, and codegrees of complex reflection groups, see the tables in Template:Harvs.
Degrees
Shephard and Todd proved that a finite group acting on a complex vector space is a complex reflection group if and only if its ring of invariants is a polynomial ring (Chevalley–Shephard–Todd theorem). For being the rank of the reflection group, the degrees of the generators of the ring of invariants are called degrees of W and are listed in the column above headed "degrees". They also showed that many other invariants of the group are determined by the degrees as follows:
- The center of an irreducible reflection group is cyclic of order equal to the greatest common divisor of the degrees.
- The order of a complex reflection group is the product of its degrees.
- The number of reflections is the sum of the degrees minus the rank.
- An irreducible complex reflection group comes from a real reflection group if and only if it has an invariant of degree 2.
Codegrees
For being the rank of the reflection group, the codegrees of W can be defined by
- For a real reflection group, the codegrees are the degrees minus 2.
- The number of reflection hyperplanes is the sum of the codegrees plus the rank.
Well-generated complex reflection groups
An irreducible complex reflection group of rank is generated by or by reflections. It is said to be well-generated if it is generated by reflections ; it is proved that this is equivalent to the property for all . For irreducible well-generated complex reflection groups, the Coxeter number is defined to be the largest degree, . A reducible complex reflection group is said to be well-generated if it is a product of irreducible well-generated complex reflection groups. Any finite real reflection group is well-generated.
References
- Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.
Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.
In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.
Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010 - Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.
Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.
In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.
Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010 - Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.
Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.
In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.
Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010 - Hiller, Howard Geometry of Coxeter groups. Research Notes in Mathematics, 54. Pitman (Advanced Publishing Program), Boston, Mass.-London, 1982. iv+213 pp. ISBN 0-273-08517-4*
- Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.
Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.
In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.
Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010 - Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.
Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.
In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.
Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010