Conjugacy classes of groups¶
This module implements a wrapper of GAP’s ConjugacyClass
function.
There are two main classes, ConjugacyClass
and
ConjugacyClassGAP
. All generic methods should go into
ConjugacyClass
, whereas ConjugacyClassGAP
should only
contain wrappers for GAP functions. ConjugacyClass
contains some
fallback methods in case some group cannot be defined as a GAP object.
Todo
 Implement a nonnaive fallback method for computing all the elements of the conjugacy class when the group is not defined in GAP, as the one in Butler’s paper.
 Define a sage method for gap matrices so that groups of matrices can use the quicker GAP algorithm rather than the naive one.
EXAMPLES:
Conjugacy classes for groups of permutations:
sage: G = SymmetricGroup(4)
sage: g = G((1,2,3,4))
sage: G.conjugacy_class(g)
Conjugacy class of cycle type [4] in Symmetric group of order 4! as a permutation group
Conjugacy classes for groups of matrices:
sage: F = GF(5)
sage: gens = [matrix(F,2,[1,2, 1, 1]), matrix(F,2, [1,1, 0,1])]
sage: H = MatrixGroup(gens)
sage: h = H(matrix(F,2,[1,2, 1, 1]))
sage: H.conjugacy_class(h)
Conjugacy class of [1 2]
[4 1] in Matrix group over Finite Field of size 5 with 2 generators (
[1 2] [1 1]
[4 1], [0 1]
)

class
sage.groups.conjugacy_classes.
ConjugacyClass
(group, element)¶ Bases:
sage.structure.parent.Parent
Generic conjugacy classes for elements in a group.
This is the default fallback implementation to be used whenever GAP cannot handle the group.
EXAMPLES:
sage: G = SymmetricGroup(4) sage: g = G((1,2,3,4)) sage: ConjugacyClass(G,g) Conjugacy class of (1,2,3,4) in Symmetric group of order 4! as a permutation group

an_element
()¶ Return a representative of
self
.EXAMPLES:
sage: G = SymmetricGroup(3) sage: g = G((1,2,3)) sage: C = ConjugacyClass(G,g) sage: C.representative() (1,2,3)

is_rational
()¶ Check if
self
is rational (closed for powers).EXAMPLES:
sage: G = SymmetricGroup(4) sage: g = G((1,2,3,4)) sage: c = ConjugacyClass(G,g) sage: c.is_rational() False

is_real
()¶ Check if
self
is real (closed for inverses).EXAMPLES:
sage: G = SymmetricGroup(4) sage: g = G((1,2,3,4)) sage: c = ConjugacyClass(G,g) sage: c.is_real() True

list
()¶ Return a list with all the elements of
self
.EXAMPLES:
Groups of permutations:
sage: G = SymmetricGroup(3) sage: g = G((1,2,3)) sage: c = ConjugacyClass(G,g) sage: L = c.list() sage: Set(L) == Set([G((1,3,2)), G((1,2,3))]) True

representative
()¶ Return a representative of
self
.EXAMPLES:
sage: G = SymmetricGroup(3) sage: g = G((1,2,3)) sage: C = ConjugacyClass(G,g) sage: C.representative() (1,2,3)

set
()¶ Return the set of elements of the conjugacy class.
EXAMPLES:
Groups of permutations:
sage: G = SymmetricGroup(3) sage: g = G((1,2)) sage: C = ConjugacyClass(G,g) sage: S = [(2,3), (1,2), (1,3)] sage: C.set() == Set(G(x) for x in S) True
Groups of matrices over finite fields:
sage: F = GF(5) sage: gens = [matrix(F,2,[1,2, 1, 1]), matrix(F,2, [1,1, 0,1])] sage: H = MatrixGroup(gens) sage: h = H(matrix(F,2,[1,2, 1, 1])) sage: C = ConjugacyClass(H,h) sage: S = [[[3, 2], [2, 4]], [[0, 1], [2, 2]], [[3, 4], [1, 4]],\ [[0, 3], [4, 2]], [[1, 2], [4, 1]], [[2, 1], [2, 0]],\ [[4, 1], [4, 3]], [[4, 4], [1, 3]], [[2, 4], [3, 0]],\ [[1, 4], [2, 1]], [[3, 3], [3, 4]], [[2, 3], [4, 0]],\ [[0, 2], [1, 2]], [[1, 3], [1, 1]], [[4, 3], [3, 3]],\ [[4, 2], [2, 3]], [[0, 4], [3, 2]], [[1, 1], [3, 1]],\ [[2, 2], [1, 0]], [[3, 1], [4, 4]]] sage: C.set() == Set(H(x) for x in S) True
It is not implemented for infinite groups:
sage: a = matrix(ZZ,2,[1,1,0,1]) sage: b = matrix(ZZ,2,[1,0,1,1]) sage: G = MatrixGroup([a,b]) # takes 1s sage: g = G(a) sage: C = ConjugacyClass(G, g) sage: C.set() Traceback (most recent call last): ... NotImplementedError: Listing the elements of conjugacy classes is not implemented for infinite groups! Use the iter function instead.


class
sage.groups.conjugacy_classes.
ConjugacyClassGAP
(group, element)¶ Bases:
sage.groups.conjugacy_classes.ConjugacyClass
Class for a conjugacy class for groups defined over GAP.
Intended for wrapping GAP methods on conjugacy classes.
INPUT:
group
– the group in which the conjugacy class is takenelement
– the element generating the conjugacy class
EXAMPLES:
sage: G = SymmetricGroup(4) sage: g = G((1,2,3,4)) sage: ConjugacyClassGAP(G,g) Conjugacy class of (1,2,3,4) in Symmetric group of order 4! as a permutation group

cardinality
()¶ Return the size of this conjugacy class.
EXAMPLES:
sage: W = WeylGroup(['C',6]) sage: cc = W.conjugacy_class(W.an_element()) sage: cc.cardinality() 3840 sage: type(cc.cardinality()) <type 'sage.rings.integer.Integer'>

set
()¶ Return a Sage
Set
with all the elements of the conjugacy class.By default attempts to use GAP construction of the conjugacy class. If GAP method is not implemented for the given group, and the group is finite, falls back to a naive algorithm.
Warning
The naive algorithm can be really slow and memory intensive.
EXAMPLES:
Groups of permutations:
sage: G = SymmetricGroup(4) sage: g = G((1,2,3,4)) sage: C = ConjugacyClassGAP(G,g) sage: S = [(1,3,2,4), (1,4,3,2), (1,3,4,2), (1,2,3,4), (1,4,2,3), (1,2,4,3)] sage: C.set() == Set(G(x) for x in S) True