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The center of the general linear group over a field F, GL n (F), is the collection of scalar matrices, { sI n ∣ s ∈ F \ {0} }. The center of the orthogonal group, O n (F) is {I n, −I n}. The center of the special orthogonal group, SO(n) is the whole group when n = 2, and otherwise {I n, −I n} when n is even, and trivial when n is odd.
The center of a group G consists of all those elements x in G such that xg = gx for all g in G. This is a normal subgroup of G. The similarly named notion for a semigroup is defined likewise and it is a subsemigroup. [1] [2] The center of a ring (or an associative algebra) R is the subset of R consisting of all those elements x of R such that ...
Another less common notation for the centralizer is Z(a), which parallels the notation for the center. With this latter notation, one must be careful to avoid confusion between the center of a group G, Z(G), and the centralizer of an element g in G, Z(g). The normalizer of S in the group (or semigroup) G is defined as
In mathematics, in the field of group theory, a subgroup of a group is termed central if it lies inside the center of the group. Given a group G {\displaystyle G} , the center of G {\displaystyle G} , denoted as Z ( G ) {\displaystyle Z(G)} , is defined as the set of those elements of the group which commute with every element of the group.
Other named normal subgroups of an arbitrary group include the center of the group (the set of elements that commute with all other elements) and the commutator subgroup [,]. [7] [8] More generally, since conjugation is an isomorphism, any characteristic subgroup is a normal subgroup. [9]
The center Z of the group SL(2, R) is a cyclic group {I, −I} of order 2, consisting of the identity matrix and its negative. On any irreducible representation, the center either acts trivially, or by the nontrivial character of Z , which represents the matrix - I by multiplication by -1 in the representation space.
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In the quaternion group of order 8, each of the cyclic subgroups of order 4 is normal, but none of these are characteristic. However, the subgroup, {1, −1}, is characteristic, since it is the only subgroup of order 2. If n > 2 is even, the dihedral group of order 2n has 3 subgroups of index 2, all of which are normal. One of these is the ...