Center (mathematics)

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Typically used for an element or a subset in a set with additional structure, satisfying certain special core properties.

In group theory

Center of a group: The set of those elements of the group that commute with every element of the group. It forms a subgroup, in fact, a characteristic subgroup.

Primary subject wiki entry: Groupprops:Center

Also located at: Wikipedia:Center (group theory)

In ring theory

Center of a ring: The set of those elements of a (usually unital) ring that commute with every element of the ring. The center of a ring is a subring; for a unital ring, it is a subring containing the multiplicative identity.

Primary subject wiki entry: Noncommutative:Center of a ring

In graph theory

Center of a graph