In mathematics, the generalized symmetric group is the wreath product S ( m , n ) := C m ≀ S n {\displaystyle S(m,n):=C_{m}\wr S_{n}} of the cyclic group of order m and the symmetric group of order n.
Examples For m = 1 , {\displaystyle m=1,} the generalized symmetric group is exactly the ordinary symmetric group: S ( 1 , n ) = S n . {\displaystyle S(1,n)=S_{n}.}
For m = 2 , {\displaystyle m=2,} one can consider the cyclic group of order 2 as positives and negatives ( C 2 ≅ { ± 1 } {\displaystyle C_{2}\cong \{\pm 1\}} ) and identify the generalized symmetric group S ( 2 , n ) {\displaystyle S(2,n)} with the signed symmetric group.
Representation theory There is a natural representation of elements of S ( m , n ) {\displaystyle S(m,n)} as generalized permutation matrices, where the nonzero entries are m-th roots of unity: C m ≅ μ m . {\displaystyle C_{m}\cong \mu _{m}.}
The representation theory has been studied since (Osima 1954); see references in (Can 1996). As with the symmetric group, the representations can be constructed in terms of Specht modules; see (Can 1996).
Homology The first group homology group – concretely, the abelianization – is C m × C 2 {\displaystyle C_{m}\times C_{2}} (for m odd this is isomorphic to C 2 m {\displaystyle C_{2m}} ): the C m {\displaystyle C_{m}} factors (which are all conjugate, hence must map identically in an abelian group, since conjugation is trivial in an abelian group) can be mapped to C m {\displaystyle C_{m}} (concretely, by taking the product of all the C m {\displaystyle C_{m}} values), while the sign map on the symmetric group yields the C 2 . {\displaystyle C_{2}.} These are independent, and generate the group, hence are the abelianization. The second homology group – in classical terms, the Schur multiplier – is given by (Davies & Morris 1974):
H 2 ( S ( 2 k + 1 , n ) ) = { 1 n < 4 Z / 2 n ≥ 4. {\displaystyle H_{2}(S(2k+1,n))={\begin{cases}1&n<4\\\mathbf {Z} /2&n\geq 4.\end{cases}}}
H 2 ( S ( 2 k + 2 , n ) ) = { 1 n = 0 , 1 Z / 2 n = 2 ( Z / 2 ) 2 n = 3 ( Z / 2 ) 3 n ≥ 4. {\displaystyle H_{2}(S(2k+2,n))={\begin{cases}1&n=0,1\\\mathbf {Z} /2&n=2\\(\mathbf {Z} /2)^{2}&n=3\\(\mathbf {Z} /2)^{3}&n\geq 4.\end{cases}}}
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