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GroupTheory

  

WreathProduct

  

form the wreath product of groups

  

RegularWreathProduct

  

form the regular wreath product of groups

 

Calling Sequence

Parameters

Description

Examples

Calling Sequence

WreathProduct( G, H, ... )

RegularWreathProduct( G, H, ... )

Parameters

G,H, ...

-

two or more permutation groups

Description

• 

Let  and  be permutation groups. The wreath product G  H_ of  by  is a permutation group constructed as a semi-direct product of  copies of  (called the base group), where  is the degree of , and the action of  on the base group is the action of  by permuting the copies of . Thus, the order of G  H_ is equal to , and the degree of the wreath product is the product of the degrees of  and .

• 

The regular wreath product of  and  is the wreath product in which  is considered as a regular permutation group on itself. (This is also called the "standard wreath product".)

• 

The WreathProduct( G, H ) command returns a permutation group that is the wreath product G  H_.

• 

If more than two groups are provided as input, then an iterated wreath product is constructed using the left associative rule. For example, WreathProduct( A, B, C, D ) returns ((A  B)  C)  D_.

• 

The RegularWreathProduct( G, H ) command returns the regular wreath product of  and . In this case, it is not required that  be a permutation group, as a regular permutation representation of the finite group  is used instead. (Here,  may be either a Cayley table group or a finitely presented finite group, as well as a permutation group, which need not be itself regular.)

Examples

(1)

(2)

Iterated wreath products appear naturally as Sylow subgroups of symmetric groups of prime power degree.

(3)

(4)

Note that iterated wreath products grow quite rapidly.

(5)

(6)

(7)

(8)

(9)

(10)

The wreath product construction is not commutative; notice that even the order is different.

(11)

Note that the regular wreath product is also different in this case, since the second argument here is not the regular permutation representation of the symmetric group.

(12)

Since both  and  are transitive, so too is their wreath product.

(13)

However, in general, the wreath product is not primitive.

(14)

(15)

Here we construct a wreath product with an intransitive second argument.

The resulting group is not transitive.

(16)

(17)

Here we construct a wreath product with an intransitive first argument.

Again, the result is an intransitive group.

(18)

(19)

(20)

(21)

(22)

(23)

(24)

(25)

(26)

Notice that, if a group is already regular, then its regular wreath product is isomorphic to the ordinary wreath product.

(27)

(28)

(29)

See Also

GroupTheory

GroupTheory[AlternatingGroup]

GroupTheory[AreIsomorphic]

GroupTheory[CyclicGroup]

GroupTheory[DihedralGroup]

GroupTheory[DirectProduct]

GroupTheory[GroupOrder]

GroupTheory[IsPrimitive]

GroupTheory[IsTransitive]

GroupTheory[Orbits]

GroupTheory[SymmetricGroup]

 


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