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#############################################################################
##
#W initperm.gi AutPGrp package Bettina Eick
##
#H @(#)$Id: initperm.gi,v 1.7 2009/08/31 07:40:15 gap Exp $
##
Revision.("autpgrp/gap/initperm_gi") :=
"@(#)$Id: initperm.gi,v 1.7 2009/08/31 07:40:15 gap Exp $";
#############################################################################
##
#F Fingerprint( G, U )
##
FingerprintSmall := function( G, U )
return Flat( [IdGroup( U ), Size(CommutatorSubgroup( G, U )) ]);
end;
FingerprintMedium := function( G, U )
local ranks, invs, comm, all, cls, fus, new;
# some general stuff
ranks := LGFirst( SpecialPcgs( U ) );
invs := AbelianInvariants( Centre(U) );
comm := Size( CommutatorSubgroup( G, U ) );
# use conjugacy classes
all := Orbits( G, AsList(U) );
all := List( all, x -> Set(x));
cls := List( all, x -> Order(x[1]) );
Sort( cls );
return Concatenation( ranks, invs, [comm], cls );
end;
FingerprintLarge := function( G, U )
return LGFirst( SpecialPcgs(U) );
end;
FingerprintHuge := function( G, U )
return List( DerivedSeries(U), Size );
end;
PGFingerprint := function ( G, U )
if Size( U ) <= 255 and IsRecord( ID_AVAILABLE( Size(U) ) ) then
return FingerprintSmall( G, U );
elif Size( U ) <= 1000 then
return FingerprintMedium( G, U );
elif Size( U ) <= 2^21 then
return FingerprintLarge( G, U );
else
return FingerprintHuge( G, U );
fi;
end;
DualBasis := function( base )
local M;
M := NullspaceMat( TransposedMat( base ));
M := List( M, ShallowCopy );
TriangulizeMat( M );
return M;
end;
#############################################################################
##
#F PartitionMinimalOvergrps ( G, pcgs, norm )
##
PartitionMinimalOvergrps := function( G, pcgs, norm )
local min, done, part, i, tup, pos;
Info( InfoAutGrp, 3, " computing partition ");
done := [];
part := [];
for i in [1..Length(norm)] do
Info( InfoAutGrp, 4, " start ",i);
#min := DualBasis( [norm[i]] );
min := InducedPcgsByBasis( pcgs, [norm[i]] );
tup := PGFingerprint( G, SubgroupByPcgs( G, min ) );
pos := Position( done, tup );
if IsBool( pos ) then
Add( part, [i] );
Add( done, tup );
else
Add( part[pos], i );
fi;
od;
Sort( part, function( x, y ) return Length(x) < Length(y); end );
return part;
end;
#############################################################################
##
#F PartitionStabilizer ( A, part, norm )
##
PartitionStabilizer := function( A, part, norm )
local iso, P, sub, gens, n, q;
Info( InfoAutGrp, 3, " computing stabilizer of ", part);
iso := ActionHomomorphism( A, norm, OnLines, "surjective" );
P := Image( iso );
# transfer size info
n := DimensionOfMatrixGroup(A);
q := Size(FieldOfMatrixGroup(A));
if HasIsNaturalGL(A) and IsNaturalGL(A) then
SetSize(P,Size(A)/(q-1));
elif HasIsNaturalSL(A) and IsNaturalSL(A) then
SetSize(P,Size(A)/Gcd(n,q-1));
fi;
# loop
for sub in part{[1..Length(part)-1]} do
if Length( sub ) = 1 then
P := Stabilizer( P, sub[1], OnPoints );
Info( InfoAutGrp, 3, " found stabilizer of size ", Size(P));
else
P := Stabilizer( P, sub, OnSets );
Info( InfoAutGrp, 3, " found stabilizer of size ", Size(P));
fi;
od;
gens := SmallGeneratingSet( P );
# return
return rec( perm := gens,
mats := List( gens, x -> PreImagesRepresentative(iso,x) ),
size := Size(P) );
end;
#############################################################################
##
#F AutoOfMat( mat, H )
##
AutoOfMat := function( mat, H )
local img, aut, pcgs;
pcgs := Pcgs(H);
img := List( mat, x -> PcElementByExponentsNC(pcgs, x) );
aut := PGAutomorphism( H, pcgs, img );
return aut;
end;
#############################################################################
##
#F InitAutomorphismGroupOver( G )
##
InstallGlobalFunction( InitAutomorphismGroupOver,
function( G )
local r, p, pcgsG, pcgsN, pcgs, base, V, norm, part, stab, H, kern, A;
Info( InfoAutGrp, 2, " initialize automorphism group: Over ");
# set up
r := RankPGroup( G );
p := PrimePGroup( G );
# pgcs'se
pcgsG := SpecialPcgs(G);
pcgsN := InducedPcgsByPcSequenceNC( pcgsG, pcgsG{[r+1..Length(pcgsG)]} );
pcgs := pcgsG mod pcgsN;
# get partition stabilizer
base := IdentityMat( r, GF(p) );
V := GF(p)^r;
norm := NormedVectors( V );
part := PartitionMinimalOvergrps( G, pcgs, norm );
stab := PartitionStabilizer( GL( r, p ), part, norm );
# get quotient
H := FrattiniQuotientPGroup( G );
kern := InitAgAutos( H, p );
# create aut grp
A := rec();
A.glAutos := List( stab.mats, x -> AutoOfMat( x, H ) );
A.glOrder := stab.size;
A.glOper := ShallowCopy( stab.perm );
A.agAutos := kern.auts;
A.agOrder := kern.rels;
A.one := IdentityPGAutomorphism(H);
A.group := H;
A.size := A.glOrder * Product( A.agOrder );
# try to construct solvable normal subgroup
NiceInitGroup( A, true );
return A;
end);
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