<!-- ********************ESSP******************** -->
<Chapter Label="ESSP">
<Heading>Shoda pairs</Heading>
<Section Label="ESSPESSP">
<Heading>Computing extremely strong Shoda pairs</Heading>
<ManSection>
<Attr Name="ExtremelyStrongShodaPairs"
Arg="G"
Comm="A list of ESSPs representatives realizing Wedderburn components of QG" />
<Returns>
A list of pairs of subgroups of the input group.
</Returns>
<Description>
The input should be a finite group <A>G</A>.
<P/>
Computes a list of representatives of the equivalence classes of
<E>extremely strong Shoda pairs</E>
(<Ref Sect="ESSPDef" />) of a finite group <A>G</A>.
<P/>
<Example>
<![CDATA[
gap> ExtremelyStrongShodaPairs(DihedralGroup(32));
[ [ <pc group of size 32 with 5 generators>,
<pc group of size 32 with 5 generators> ],
[ <pc group of size 32 with 5 generators>,
Group([ f1*f2*f3*f4*f5, f3, f4, f5 ]) ],
[ <pc group of size 32 with 5 generators>, Group([ f2, f3, f4, f5 ]) ],
[ <pc group of size 32 with 5 generators>, Group([ f1, f3, f4, f5 ]) ],
[ Group([ f1*f2*f3*f4*f5, f3, f4, f5 ]), Group([ f1*f2*f4*f5, f4, f5 ]) ],
[ Group([ f2, f3, f4, f5 ]), Group([ f5 ]) ],
[ Group([ f2, f3, f4, f5 ]), Group([ ]) ] ]
gap> ExtremelyStrongShodaPairs(SL(2,3));
[ [ SL(2,3), SL(2,3) ],
[ SL(2,3),
Group([ [ [ Z(3)^0, Z(3)^0 ], [ Z(3)^0, Z(3) ] ],
[ [ Z(3), Z(3)^0 ], [ Z(3)^0, Z(3)^0 ] ],
[ [ Z(3), 0*Z(3) ], [ 0*Z(3), Z(3) ] ] ]) ],
[
Group([ [ [ Z(3)^0, Z(3)^0 ], [ Z(3)^0, Z(3) ] ],
[ [ Z(3), Z(3)^0 ], [ Z(3)^0, Z(3)^0 ] ],
[ [ Z(3), 0*Z(3) ], [ 0*Z(3), Z(3) ] ] ]),
Group([ [ [ 0*Z(3), Z(3) ], [ Z(3)^0, 0*Z(3) ] ],
[ [ Z(3), 0*Z(3) ], [ 0*Z(3), Z(3) ] ] ]) ] ]
gap> ExtremelyStrongShodaPairs(SymmetricGroup(5));
[ [ Sym( [ 1 .. 5 ] ), Sym( [ 1 .. 5 ] ) ],
[ Sym( [ 1 .. 5 ] ), Alt( [ 1 .. 5 ] ) ] ]
]]>
</Example>
</Description>
</ManSection>
</Section>
<Heading>Strong Shoda pairs</Heading>
<Section Label="SSPSSP">
<Heading>Computing strong Shoda pairs</Heading>
<ManSection>
<Attr Name="StrongShodaPairs"
Arg="G"
Comm="A list of SSPs representatives realizing Wedderburn components of QG" />
<Returns>
A list of pairs of subgroups of the input group.
</Returns>
<Description>
The input should be a finite group <A>G</A>.
<P/>
Computes a list of representatives of the equivalence classes of
<E>strong Shoda pairs</E>
(<Ref Sect="SSPDef" />) of a finite group <A>G</A>.
<P/>
<Example>
<![CDATA[
gap> ssp:=StrongShodaPairs( SymmetricGroup(4) );;
gap> Length(ssp);
5
gap> List(ssp,x->List(x,StructureDescription));
[ [ "S4", "S4" ], [ "S4", "A4" ], [ "A4", "C2 x C2" ], [ "D8", "C2 x C2" ],
[ "D8", "C4" ] ]
gap> ssp:=StrongShodaPairs( DihedralGroup(64) );;
gap> Length(ssp);
8
gap> List(ssp,x->List(x,StructureDescription));
[ [ "D64", "D64" ], [ "D64", "D32" ], [ "D64", "C32" ], [ "D64", "D32" ],
[ "D32", "D16" ], [ "C32", "C4" ], [ "C32", "C2" ], [ "C32", "1" ] ]
]]>
</Example>
</Description>
</ManSection>
</Section>
<Section Label="IsSSP">
<Heading>Properties related with Shoda pairs</Heading>
<ManSection>
<Oper Name="IsExtremelyStrongShodaPair"
Arg="G K H"
Comm="Is (K,H) an extremely strong Shoda pair of G?" />
<Description>
The first argument should be a finite group <A>G</A>,
the second one a normal sugroup <A>K</A> of <A>G</A> and the
third one a subgroup of <A>K</A>. <P/>
Returns <K>true</K> if (<A>K</A>,<A>H</A>) is an
<E>extremely strong Shoda pair</E> (<Ref Sect="ESSPDef" />)
of <A>G</A>, and <K>false</K> otherwise.
<Example>
<![CDATA[
gap> G:=SymmetricGroup(4);; K:=Group( (1,3,2,4), (3,4) );;
gap> H1:=Group( (2,4,3), (1,4)(2,3), (1,3)(2,4) );;
gap> H2:=Group( (3,4), (1,2)(3,4) );;
gap> IsExtremelyStrongShodaPair( G, G, H1 );
true
gap> IsExtremelyStrongShodaPair( G, K, H2 );
false
gap> IsExtremelyStrongShodaPair( G, G, H2 );
false
gap> IsExtremelyStrongShodaPair( G, G, K );
false
]]>
</Example>
</Description>
</ManSection>
<ManSection>
<Oper Name="IsStrongShodaPair"
Arg="G K H"
Comm="Is (K,H) a strong Shoda pair of G?" />
<Description>
The first argument should be a finite group <A>G</A>,
the second one a sugroup <A>K</A> of <A>G</A> and the
third one a subgroup of <A>K</A>. <P/>
Returns <K>true</K> if (<A>K</A>,<A>H</A>) is a
<E>strong Shoda pair</E> (<Ref Sect="SSPDef" />)
of <A>G</A>, and <K>false</K> otherwise. <P/>
Note that every extremely strong Shoda pair is a strong Shoda pair,
but the converse is not true.
<Example>
<![CDATA[
gap> G:=SymmetricGroup(4);; K:=Group( (1,3,2,4), (3,4) );;
gap> H1:=Group( (2,4,3), (1,4)(2,3), (1,3)(2,4) );;
gap> H2:=Group( (3,4), (1,2)(3,4) );;
gap> IsStrongShodaPair( G, G, H1 );
true
gap> IsExtremelyStrongShodaPair( G, K, H2 );
false
gap> IsStrongShodaPair( G, K, H2 );
true
gap> IsStrongShodaPair( G, G, K );
false
]]>
</Example>
</Description>
</ManSection>
<ManSection>
<Oper Name="IsShodaPair"
Arg="G K H"
Comm="Is (K,H) a Shoda pair of G?" />
<Description>
The first argument should be a finite group <A>G</A>,
the second a subgroup <A>K</A> of <A>G</A> and the
third one a subgroup of <A>K</A>. <P/>
Returns <K>true</K> if (<A>K</A>,<A>H</A>) is a
<E>Shoda pair</E> (<Ref Sect="SPDef" />) of <A>G</A>.<P/>
Note that every strong Shoda pair is a Shoda pair,
but the converse is not true.
<Example>
<![CDATA[
gap> G:=AlternatingGroup(5);;
gap> K:=AlternatingGroup(4);;
gap> H := Group( (1,2)(3,4), (1,3)(2,4) );;
gap> IsStrongShodaPair( G, K, H );
false
gap> IsShodaPair( G, K, H );
true
]]>
</Example>
</Description>
</ManSection>
<Alt Only="LaTeX">\newpage</Alt>
<ManSection>
<Oper Name="IsStronglyMonomial"
Arg="G"
Comm="Is every irreducible character strongly monomial" />
<Description>
The input <A>G</A> should be a finite group. <P/>
Returns <K>true</K> if <A>G</A> is a <E>strongly monomial</E>
(<Ref Sect="StMon" />) finite group.
<Example>
<![CDATA[
gap> S4:=SymmetricGroup(4);;
gap> IsStronglyMonomial(S4);
true
gap> G:=SmallGroup(24,3);;
gap> IsStronglyMonomial(G);
false
gap> IsMonomial(G);
false
gap> G:=SmallGroup(1000,86);;
gap> IsMonomial(G);
true
gap> IsStronglyMonomial(G);
false
]]>
</Example>
</Description>
</ManSection>
<ManSection>
<Oper Name="IsNormallyMonomial"
Arg="G"
Comm="Is every irreducible character normally monomial" />
<Description>
The input <A>G</A> should be a finite group. <P/>
Returns <K>true</K> if <A>G</A> is a finite <E>normally monomial</E>
(<Ref Sect="NorMon" />) group.
<Example>
<![CDATA[
gap> D24:=DihedralGroup(24);
<pc group of size 24 with 4 generators>
gap> IsNormallyMonomial(D24);
true
gap> G:=SmallGroup(192,1023);
<pc group of size 192 with 7 generators>
gap> IsNormallyMonomial(G);
true
gap> G:=SmallGroup(1029,12);
<pc group of size 1029 with 4 generators>
gap> IsNormallyMonomial(G);
false
gap> IsStronglyMonomial(G);
true
gap> G:=SL(2,3);
SL(2,3)
gap> IsNormallyMonomial(G);
false
gap> IsStronglyMonomial(G);
false
]]>
</Example>
</Description>
</ManSection>
</Section>
</Chapter>
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