Difference between revisions of "Conjugacy class"
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| − | <font color="blue">Classe de conjugaison</font> (''Fr'') | + | <font color="blue">Classe de conjugaison</font> (''Fr''). <font color="red">Konjugationsklasse</font> (''Ge''). <font color="green">Clase de conjugación</font> (''Sp''). <font color="black">Classe coniugata</font> (''It''). <font color="brown">Класс сопряжённости</font> (''Ru''). <font color="purple">共役類</font> (''Ja''). |
| − | If g<sub>1</sub> and g<sub>2</sub> are two elements of a group G, they are called '''conjugate''' if there exists an element g<sub>3</sub> in G such that: | + | If ''g''<sub>1</sub> and ''g''<sub>2</sub> are two elements of a group ''G'', they are called '''conjugate''' if there exists an element ''g''<sub>3</sub> in ''G'' such that: |
| − | ::: g<sub>3</sub>g<sub>1</sub>g<sub>3</sub><sup> | + | ::: ''g''<sub>3</sub>''g''<sub>1</sub>''g''<sub>3</sub><sup>−1</sup> = ''g''<sub>2</sub>. |
| − | Conjugacy is an equivalence relation and therefore partitions G into equivalence classes: every element of the group belongs to precisely one conjugacy class | + | Conjugacy is an equivalence relation and therefore partitions ''G'' into equivalence classes: every element of the group belongs to precisely one conjugacy class. |
| + | The equivalence class that contains the element ''g''<sub>1</sub> in ''G'' is | ||
| − | + | :::Cl(''g''<sub>1</sub>) = { ''g''<sub>3</sub>''g''<sub>1</sub>''g''<sub>3</sub><sup>−1</sup>| ''g''<sub>3</sub> ∈ ''G''} | |
| − | + | and is called the '''conjugacy class''' of ''g''<sub>1</sub>. The '''class number''' of ''G'' is the number of conjugacy classes. | |
| − | |||
| − | and is called the '''conjugacy class''' of g<sub>1</sub>. The '''class number''' of G is the number of conjugacy classes | ||
| − | |||
| − | |||
| + | The classes Cl(''g''<sub>1</sub>) and Cl(''g''<sub>2</sub>) are equal if and only if ''g''<sub>1</sub> and ''g''<sub>2</sub> are conjugate, and disjoint otherwise. | ||
For [[Abelian group]]s the concept is trivial, since each element forms a class on its own. | For [[Abelian group]]s the concept is trivial, since each element forms a class on its own. | ||
[[Category:Fundamental crystallography]] | [[Category:Fundamental crystallography]] | ||
Revision as of 10:42, 13 May 2017
Classe de conjugaison (Fr). Konjugationsklasse (Ge). Clase de conjugación (Sp). Classe coniugata (It). Класс сопряжённости (Ru). 共役類 (Ja).
If g1 and g2 are two elements of a group G, they are called conjugate if there exists an element g3 in G such that:
- g3g1g3−1 = g2.
Conjugacy is an equivalence relation and therefore partitions G into equivalence classes: every element of the group belongs to precisely one conjugacy class.
The equivalence class that contains the element g1 in G is
- Cl(g1) = { g3g1g3−1| g3 ∈ G}
and is called the conjugacy class of g1. The class number of G is the number of conjugacy classes.
The classes Cl(g1) and Cl(g2) are equal if and only if g1 and g2 are conjugate, and disjoint otherwise.
For Abelian groups the concept is trivial, since each element forms a class on its own.