LESSWRONG
LW

1384
Wikitags

Conjugacy classes of the alternating group on five elements

Edited by Patrick Stevens last updated 18th Jun 2016
Requires: Alternating group, Splitting conjugacy classes in alternating group, Conjugacy classes of the symmetric group on five elements, Conjugacy class

This page lists the conjugacy classes of the alternating group A5 on five elements. See a different lens for a derivation of this result using less theory.

A5 has size 5!/2=60, where the exclamation mark denotes the factorial function. We will assume access to the conjugacy class table of S5 the symmetric group on five elements; A5 is a quotient of S5 by the sign homomorphism.

We have that a conjugacy class splits if and only if its cycle type is all odd, all distinct. (Proof.) This makes the classification of conjugacy classes very easy.

The table

We must remove all the lines of S5's table which correspond to odd permutations (that is, those which are the product of odd-many transpositions). Indeed, those lines are classes which are not even in A5.

We are left with cycle types (5), (3,1,1), (2,2,1), (1,1,1,1,1). Only the (5) cycle type can split into two, by the splitting condition. It splits into the class containing (12345) and the class which is (12345) conjugated by odd permutations in S5. A representative for that latter class is (12)(12345)(12)−1=(21345).

RepresentativeSize of classCycle typeOrder of element(12345)1255(21345)1255(123)203,1,13(12)(34)152,2,12e11,1,1,1,11

Parents:
Alternating group
Discussion
Discussion