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centralizer and normalizer

Definition/Summary
The centralizer C(a) of an element a of G is the set of all elements of G that commute with a.

The centralizer C(H) of a subgroup H of G is the set of all elements of G that commute with every element of H.

The normalizer N(H) of a subgroup H of G is the set of all elements of G under which H is self-conjugate.

The center of a group is the group's centralizer, while a group's normalizer is itself.

Equations
Centralizer of element a:
[itex]C(a) = \{g \in G | ga = ag \}[/itex]

The order of an element's centralizer and the order of its conjugacy class multiply to get the order of the group.

Centralizer of subgroup H:
[itex]C(H) = \{g \in G | gh = hg ,\ \forall h \in H \}[/itex]

Normalizer of subgroup H:
[itex]N(H) = \{g \in G | gh = h'g ,\ h' \in H ,\ \forall h \in H \}[/itex]

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Breakdown
Mathematics
> Algebra
>> Group Theory

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