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''in a group $G$''
 
''in a group $G$''
  
Elements <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025010/c0250102.png" /> and <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025010/c0250103.png" /> of <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025010/c0250104.png" /> for which
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Elements $x$ and $x'$ of $G$ for which
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$$
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x' = g^{-1} x g
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$$
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for some $g$ in $G$. One also says that $x'$ is the result of conjugating $x$ by $g$. The power notation $x^g$ is frequently used for the conjugate of $x$ under $g$.
  
<table class="eq" style="width:100%;"> <tr><td valign="top" style="width:94%;text-align:center;"><img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025010/c0250105.png" /></td> </tr></table>
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Let $A,B$ be two subsets of a group $G$, then $A^B$ denotes the set
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$$
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\{ a^b : a \in A\,,\, b \in B \}
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$$
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For some fixed $g$ in $G$ and some subset $M$ of $G$ the set $M^g = \{ m^g : m \in M\}$ is said to be conjugate to the set $M$ in $G$. In particular, two subgroups $U$ and $V$ are called conjugate subgroups if $V = U^g$ for some $g$ in $G$. If a subgroup $H$ coincides with $H^g$ for every $g \in G$ (that is, $H$ consists of all conjugates of all its elements), then $H$ is called a ''[[normal subgroup]]'' of $G$ (or an invariant subgroup, or, rarely, a self-conjugate subgroup).
  
for some <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025010/c0250106.png" /> in <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025010/c0250107.png" />. One also says that <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025010/c0250108.png" /> is the result of conjugating <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025010/c0250109.png" /> by <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025010/c02501010.png" />. The power notation <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025010/c02501011.png" /> is frequently used for the conjugate of <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025010/c02501012.png" /> under <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025010/c02501013.png" />.
 
  
Let <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025010/c02501014.png" /> be two subsets of a group <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025010/c02501015.png" />, then <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025010/c02501016.png" /> denotes the set
 
  
<table class="eq" style="width:100%;"> <tr><td valign="top" style="width:94%;text-align:center;"><img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025010/c02501017.png" /></td> </tr></table>
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====Comments====
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Conjugacy of elements is an [[equivalence relation]] on $G$, and the equivalence classes are the ''conjugacy classes'' of $G$.
  
For some fixed <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025010/c02501018.png" /> in <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025010/c02501019.png" /> and some subset <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025010/c02501020.png" /> of <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025010/c02501021.png" /> the set <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025010/c02501022.png" /> is said to be conjugate to the set <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025010/c02501023.png" /> in <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025010/c02501024.png" />. In particular, two subgroups <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025010/c02501025.png" /> and <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025010/c02501026.png" /> are called conjugate subgroups if <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025010/c02501027.png" /> for some <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025010/c02501028.png" /> in <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025010/c02501029.png" />. If a subgroup <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025010/c02501030.png" /> coincides with <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025010/c02501031.png" /> for every <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025010/c02501032.png" /> (that is, <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025010/c02501033.png" /> consists of all conjugates of all its elements), then <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025010/c02501034.png" /> is called a [[Normal subgroup|normal subgroup]] of <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/c/c025/c025010/c02501035.png" /> (or an invariant subgroup, or, rarely, a self-conjugate subgroup).
 
 
 
 
====Comments====
 
 
The map $x \mapsto g^{-1} x g$ for given $g$ is ''conjugation by $g$'': it is an [[inner automorphism]] of $G$.
 
The map $x \mapsto g^{-1} x g$ for given $g$ is ''conjugation by $g$'': it is an [[inner automorphism]] of $G$.
  
  
 
====References====
 
====References====
<table><TR><TD valign="top">[a1]</TD> <TD valign="top">  B. Huppert,  "Endliche Gruppen" , '''1''' , Springer  (1967)</TD></TR><TR><TD valign="top">[a2]</TD> <TD valign="top">  D. Gorenstein,  "Finite groups" , Chelsea, reprint  (1980)</TD></TR></table>
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<table>
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<TR><TD valign="top">[a1]</TD> <TD valign="top">  B. Huppert,  "Endliche Gruppen" , '''1''' , Springer  (1967)</TD></TR>
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<TR><TD valign="top">[a2]</TD> <TD valign="top">  D. Gorenstein,  "Finite groups" , Chelsea, reprint  (1980)</TD></TR>
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</table>

Latest revision as of 21:08, 29 November 2014

2020 Mathematics Subject Classification: Primary: 20-XX [MSN][ZBL] in a group $G$

Elements $x$ and $x'$ of $G$ for which $$ x' = g^{-1} x g $$ for some $g$ in $G$. One also says that $x'$ is the result of conjugating $x$ by $g$. The power notation $x^g$ is frequently used for the conjugate of $x$ under $g$.

Let $A,B$ be two subsets of a group $G$, then $A^B$ denotes the set $$ \{ a^b : a \in A\,,\, b \in B \} $$ For some fixed $g$ in $G$ and some subset $M$ of $G$ the set $M^g = \{ m^g : m \in M\}$ is said to be conjugate to the set $M$ in $G$. In particular, two subgroups $U$ and $V$ are called conjugate subgroups if $V = U^g$ for some $g$ in $G$. If a subgroup $H$ coincides with $H^g$ for every $g \in G$ (that is, $H$ consists of all conjugates of all its elements), then $H$ is called a normal subgroup of $G$ (or an invariant subgroup, or, rarely, a self-conjugate subgroup).


Comments

Conjugacy of elements is an equivalence relation on $G$, and the equivalence classes are the conjugacy classes of $G$.

The map $x \mapsto g^{-1} x g$ for given $g$ is conjugation by $g$: it is an inner automorphism of $G$.


References

[a1] B. Huppert, "Endliche Gruppen" , 1 , Springer (1967)
[a2] D. Gorenstein, "Finite groups" , Chelsea, reprint (1980)
How to Cite This Entry:
Conjugate elements. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Conjugate_elements&oldid=35117
This article was adapted from an original article by O.A. Ivanova (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article