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#############################################################################
##
#W cpcs.gi POLENTA package Bjoern Assmann
##
## Methods for the calculation of
## constructive pc-sequences for rational matrix groups
##
#Y 2003
##
#############################################################################
##
#F CPCS_PRMGroup( arg )
##
## arg[1] = G is a rational polycyclic rational matrix group
##
InstallGlobalFunction( CPCS_PRMGroup , function( arg )
local G;
G := arg[1];
if IsAbelian( G ) then
return CPCS_AbelianPRMGroup( G );
else
if IsBound( arg[2] ) then
return CPCS_NonAbelianPRMGroup( arg[1], arg[2] );
else
return CPCS_NonAbelianPRMGroup( G );
fi;
fi;
end );
#############################################################################
##
#F CPCS_NonAbelianPRMGroup( arg )
##
## arg[1] = G is an non-abelian polycyclic rational matrix group
##
InstallGlobalFunction( CPCS_NonAbelianPRMGroup , function( arg )
local p, d, gens_p,G, bound_derivedLength, pcgs_I_p, gens_K_p,
gens_K_p_m, gens, gens_K_p_mutableCopy, pcgs,
gensOfBlockAction, pcgs_nue_K_p, pcgs_GU, gens_U_p, pcgs_U_p,
radSeries, comSeries, recordSeries, isTriang, isFiniteGen,
testIsPoly;
# setup
G := arg[1];
gens := GeneratorsOfGroup( G );
d := Length(gens[1][1]);
Info( InfoPolenta, 1, "Determine a constructive polycyclic sequence\n",
" for the input group ..." );
Info( InfoPolenta, 1, " " );
# determine an admissible prime or take the wished one
if (Length( arg )) >= 2 and (arg[2] <> 0 ) then
p := arg[2];
else
p := DetermineAdmissiblePrime(gens);
fi;
Info( InfoPolenta, 1, "Chosen admissible prime: " , p );
Info( InfoPolenta, 1, " " );
# check whether this function is used for testing if G is polycyclic
testIsPoly := false;
if Length( arg ) = 3 then
if arg[3] = "testIsPoly" then
testIsPoly := true;
fi;
fi;
# calculate the gens of the group phi_p(<gens>) where phi_p is
# natural homomorphism to GL(d,p)
gens_p := InducedByField( gens, GF(p) );
# determine an upper bound for the derived length of G
bound_derivedLength := d+2;
# finite part
Info( InfoPolenta, 1,"Determine a constructive polycyclic sequence\n",
" for the image under the p-congruence homomorphism ..." );
pcgs_I_p := CPCS_finite_word( gens_p, bound_derivedLength );
if pcgs_I_p = fail then return fail; fi;
Info(InfoPolenta,1,"finished.");
Info( InfoPolenta, 1, "Finite image has relative orders ",
RelativeOrdersPcgs_finite( pcgs_I_p ), "." );
Info( InfoPolenta, 1, " " );
# compute the normal the subgroup gens. for the kernel of phi_p
Info( InfoPolenta, 1,"Compute normal subgroup generators for the kernel\n",
" of the p-congruence homomorphism ...");
gens_K_p := POL_NormalSubgroupGeneratorsOfK_p( pcgs_I_p, gens );
gens_K_p := Filtered( gens_K_p, x -> not x = IdentityMat(d) );
Info( InfoPolenta, 1,"finished.");
Info( InfoPolenta, 2,"The normal subgroup generators are" );
Info( InfoPolenta, 2, gens_K_p );
Info( InfoPolenta, 1, " " );
# if the input group was finite gens_K_p is an empty list
if Length( gens_K_p ) = 0 then Add( gens_K_p, gens[1]^0 );fi;
# radical series
Info( InfoPolenta, 1, "Compute the radical series ...");
gens_K_p_mutableCopy := CopyMatrixList( gens_K_p );
recordSeries := POL_RadicalSeriesNormalGensFullData( gens,
gens_K_p_mutableCopy,
d );
if recordSeries = fail then return fail; fi;
radSeries := recordSeries.sers;
Info( InfoPolenta, 1,"finished.");
Info( InfoPolenta, 1, "The radical series has length ",
Length( radSeries ), "." );
Info( InfoPolenta, 2, "The radical series is" );
Info( InfoPolenta, 2, radSeries );
Info( InfoPolenta, 1, " " );
# test if G is unipotent by abelian
isTriang := POL_TestIsUnipotenByAbelianGroupByRadSeries( gens, radSeries );
if isTriang then
Info( InfoPolenta, 1, "Group is triangularizable!" );
return CPCS_UnipotentByAbelianGroupByRadSeries( gens,
recordSeries,
testIsPoly );
fi;
# compositions series
Info( InfoPolenta, 1, "Compute the composition series ...");
comSeries := POL_CompositionSeriesByRadicalSeries( gens_K_p_mutableCopy,
d,
recordSeries.sersFullData,
1 );
if comSeries=fail then return fail; fi;
Info( InfoPolenta, 1,"finished.");
Info( InfoPolenta, 1, "The composition series has length ",
Length( comSeries ), "." );
Info( InfoPolenta, 2, "The composition series is" );
Info( InfoPolenta, 2, comSeries );
Info( InfoPolenta, 1, " " );
# induce K_p to the factors of the composition series
gensOfBlockAction := POL_InducedActionToSeries(gens_K_p, comSeries);
# let nue be the homomorphism which induces the action of K_p to
# the factors of the series
Info( InfoPolenta, 1, "Compute a constructive polycyclic sequence\n",
" for the induced action of the kernel to the composition series ...");
pcgs_nue_K_p := CPCS_AbelianSSBlocks_ClosedUnderConj( gens_K_p,
gens, comSeries );
if pcgs_nue_K_p = fail then return fail; fi;
Info(InfoPolenta,1,"finished.");
# update generators of K_p
gens_K_p := pcgs_nue_K_p.gens_K_p;
pcgs_nue_K_p := pcgs_nue_K_p.pcgs_nue_K_p;
Info( InfoPolenta, 1, "This polycyclic sequence has relative orders ",
pcgs_nue_K_p.relOrders, "." );
Info( InfoPolenta, 1, " " );
# constructive pc-sequence for G/U_p
pcgs_GU := CPCS_FactorGU_p( gens, pcgs_I_p, gens_K_p,
pcgs_nue_K_p, comSeries, p );
# normal subgroup generators for U_p
Info( InfoPolenta, 1, "Calculate normal subgroup generators for the",
"\n unipotent part ..." );
gens_U_p := POL_NormalSubgroupGeneratorsU_p( pcgs_GU, gens, gens_K_p );
Info( InfoPolenta, 1, "finished." );
Info( InfoPolenta, 2,
"The normal subgroup generators for the unipotent part are" );
Info( InfoPolenta, 2, gens_U_p );
Info( InfoPolenta, 1, " " );
# test whether U_p is finitely generated.
Info( InfoPolenta, 3, "Testing wheter U_p is finitely generated ..." );
isFiniteGen := POL_IsFinitelgeneratedU_p( gens_U_p, gens, pcgs_GU.pcs );
Info( InfoPolenta, 3, "... finished" );
if testIsPoly then
return isFiniteGen;
fi;
if not isFiniteGen then
return fail;
fi;
Info( InfoPolenta, 3, " " );
# determine a constructive pc-sequence for the unipotent group U_p
Info( InfoPolenta, 1 ,"Determine a constructive polycyclic sequence\n",
" for the unipotent part ...");
pcgs_U_p := CPCS_Unipotent_Conjugation( gens, gens_U_p );
if pcgs_U_p = fail then return fail; fi;
Info(InfoPolenta,1,"finished.");
Info(InfoPolenta,1, "The unipotent part has relative orders ");
Info(InfoPolenta,1, pcgs_U_p.rels, "." );
Info( InfoPolenta, 1, " " );
# construct a pcs for the hole group
pcgs := POL_MergeCPCS( pcgs_U_p, pcgs_GU);
Info( InfoPolenta, 1, "... computation of a constructive \n",
" polycyclic sequence for the whole group finished." );
return pcgs;
end );
#############################################################################
##
#F CPCS_AbelianPRMGroup( G )
##
## G is an abelian rational polycyclic rational matrix group
##
InstallGlobalFunction( CPCS_AbelianPRMGroup , function( G )
local p, d, gens_p, bound_derivedLength, pcgs_I_p, gens_K_p,
comSeries, gens, gens_mutableCopy, pcgs,
gensOfBlockAction, pcgs_nue_K_p, pcgs_GU, gens_U_p, pcgs_U_p;
# setup
gens := GeneratorsOfGroup( G );
d := Length(gens[1][1]);
Info( InfoPolenta, 1, "Determine a constructive polycyclic sequence\n",
" for the input group ..." );
Info( InfoPolenta, 1, " " );
# skip the the p-congruence homomorphism
pcgs_I_p := rec( gens := [], relOrders := [], wordGens := []);
p := 0;
# composition series
Info( InfoPolenta, 1, "Compute the composition series ...");
gens_mutableCopy := CopyMatrixList( gens );
comSeries := POL_CompositionSeriesAbelianRMGroup( gens_mutableCopy, d );
if comSeries = fail then return fail; fi;
Info( InfoPolenta, 1,"finished.");
Info( InfoPolenta, 1, "The composition series has length ",
Length( comSeries ), "." );
Info( InfoPolenta, 2, "The composition series is" );
Info( InfoPolenta, 2, comSeries );
Info( InfoPolenta, 1, " " );
# induce gens to the factors of the composition series
gensOfBlockAction := POL_InducedActionToSeries(gens, comSeries);
# let nue be the homomorphism which induces the action of G to
# the factors of the series
Info( InfoPolenta, 1, "Compute a constructive polycyclic sequence\n",
" for the induced action of the group to the composition series ...");
pcgs_nue_K_p := CPCS_AbelianSSBlocks( gensOfBlockAction );
Info(InfoPolenta,1,"finished.");
Info( InfoPolenta, 1, "This polycyclic sequence has relative orders ",
pcgs_nue_K_p.relOrders, "." );
Info( InfoPolenta, 1, " " );
# constructive pc-sequence for G/U_p
pcgs_GU := CPCS_FactorGU_p( gens, pcgs_I_p, gens,
pcgs_nue_K_p, comSeries, p );
# normal subgroup generators for U_p
Info( InfoPolenta, 1, "Calculate normal subgroup generators for the",
"\n unipotent part ..." );
gens_U_p := POL_NormalSubgroupGeneratorsU_p( pcgs_GU, gens, gens );
Info( InfoPolenta, 1, "finished." );
Info( InfoPolenta, 2,
"The normal subgroup generators for the unipotent part are");
Info( InfoPolenta, 2, gens_U_p );
Info( InfoPolenta, 1, " " );
# determine a constructive pc-sequence for the unipotent group U_p
Info( InfoPolenta, 1 ,"Determine a constructive polycyclic sequence\n",
" for the unipotent part ...");
pcgs_U_p := CPCS_Unipotent_Conjugation( gens, gens_U_p );
if pcgs_U_p = fail then return fail; fi;
Info(InfoPolenta,1,"finished.");
Info(InfoPolenta,1, "The unipotent part has relative orders ");
Info(InfoPolenta,1, pcgs_U_p.rels, "." );
Info( InfoPolenta, 1, " " );
# construct a pcs for the hole group
pcgs := POL_MergeCPCS( pcgs_U_p, pcgs_GU);
Info( InfoPolenta, 1, "... computation of a constructive \n",
" polycyclic sequence for the whole group finished." );
return pcgs;
end );
#############################################################################
##
#F CPCS_UnipotentByAbelianGroupByRadSeries( gens, recordSeries, testIsPoly )
##
## G is an abelian rational polycyclic rational matrix group
##
InstallGlobalFunction( CPCS_UnipotentByAbelianGroupByRadSeries ,
function( gens, recordSeries, testIsPoly )
local p, d, gens_p, bound_derivedLength, pcgs_I_p, gens_K_p,
comSeries, gens_mutableCopy, pcgs,
gensOfBlockAction, pcgs_nue_K_p, pcgs_GU, gens_U_p, pcgs_U_p,
isFiniteGen;
# setup
d := Length(gens[1][1]);
# skip the the p-congruence homomorphism
pcgs_I_p := rec( gens := [], relOrders := [], wordGens := []);
p := 0;
gens_mutableCopy := CopyMatrixList( gens );
# compositions series
Info( InfoPolenta, 1, "Compute the composition series ...");
comSeries := POL_CompositionSeriesByRadicalSeriesRecalAlg(
gens_mutableCopy,
d,
recordSeries.sersFullData,
1 );
if comSeries=fail then return fail; fi;
Info( InfoPolenta, 1,"finished.");
Info( InfoPolenta, 1, "The composition series has length ",
Length( comSeries ), "." );
Info( InfoPolenta, 2, "The composition series is" );
Info( InfoPolenta, 2, comSeries );
Info( InfoPolenta, 1, " " );
# induce gens to the factors of the composition series
gensOfBlockAction := POL_InducedActionToSeries(gens, comSeries);
# let nue be the homomorphism which induces the action of G to
# the factors of the series
Info( InfoPolenta, 1, "Compute a constructive polycyclic sequence\n",
" for the induced action of the group to the composition series ...");
pcgs_nue_K_p := CPCS_AbelianSSBlocks( gensOfBlockAction );
Info(InfoPolenta,1,"finished.");
Info( InfoPolenta, 1, "This polycyclic sequence has relative orders ",
pcgs_nue_K_p.relOrders, "." );
Info( InfoPolenta, 1, " " );
# constructive pc-sequence for G/U_p
pcgs_GU := CPCS_FactorGU_p( gens, pcgs_I_p, gens,
pcgs_nue_K_p, comSeries, p );
# normal subgroup generators for U_p
Info( InfoPolenta, 1, "Calculate normal subgroup generators for the",
"\n unipotent part ..." );
gens_U_p := POL_NormalSubgroupGeneratorsU_p( pcgs_GU, gens, gens );
Info( InfoPolenta, 1, "finished." );
Info( InfoPolenta, 2,
"The normal subgroup generators for the unipotent part are" );
Info( InfoPolenta, 2, gens_U_p );
Info( InfoPolenta, 1, " " );
# test whether U_p is finitely generated.
Info( InfoPolenta, 3, "Testing wheter U_p is finitely generated ..." );
isFiniteGen := POL_IsFinitelgeneratedU_p( gens_U_p, gens, pcgs_GU.pcs );
Info( InfoPolenta, 3, "... finished" );
if testIsPoly then
return isFiniteGen;
fi;
if not isFiniteGen then
return fail;
fi;
Info( InfoPolenta, 3, " " );
# determine a constructive pc-sequence for the unipotent group U_p
Info( InfoPolenta, 1 ,"Determine a constructive polycyclic sequence\n",
" for the unipotent part ...");
pcgs_U_p := CPCS_Unipotent_Conjugation( gens, gens_U_p );
if pcgs_U_p = fail then return fail; fi;
Info(InfoPolenta,1,"finished.");
Info(InfoPolenta,1, "The unipotent part has relative orders ");
Info(InfoPolenta,1, pcgs_U_p.rels, "." );
Info( InfoPolenta, 1, " " );
# construct a pcs for the hole group
pcgs := POL_MergeCPCS( pcgs_U_p, pcgs_GU);
Info( InfoPolenta, 1, "... computation of a constructive \n",
" polycyclic sequence for the whole group finished." );
return pcgs;
end );
#############################################################################
##
#F CPCS_FactorGU_p( gens, pcgs_I_p, gens_K_p, pcgs_nue_K_p, radicalSeries,p)
##
## calculates a constructive pcs for the G/U_p(G)
##
InstallGlobalFunction( CPCS_FactorGU_p ,
function( gens, pcgs_I_p, gens_K_p, pcgs_nue_K_p, radicalSeries,p)
local i,preImgsNue,preImgsI_p,pcs;
# calculate preimages of the pcs of K_p(G)/U_p(G) which is
# isomorphic to nue(K_p(G))
preImgsNue := POL_PreImagesPcsNueK_p_G( gens_K_p, pcgs_nue_K_p);
# calculate the preimages of the pcs of G/K_p(G) which is isomorphic
# to I_p_G
preImgsI_p := POL_PreImagesPcsI_p_G( pcgs_I_p, gens);
# Attention in preImgsI_p we have a reversed order of the pcs so
preImgsI_p := Reversed( preImgsI_p );
Assert( 2, TestPOL_PreImagesPcsI_p_G( preImgsI_p, p, pcgs_I_p ),
"error in the calculation of the preimages of I_p");
# now we have the new pcs for G/U_p
pcs := Concatenation( preImgsI_p, preImgsNue);
return rec( preImgsI_p := preImgsI_p,
preImgsNue := preImgsNue,
pcs := pcs,
p := p,
radicalSeries := radicalSeries,
pcgs_I_p := pcgs_I_p,
pcgs_nue_K_p := pcgs_nue_K_p );
end );
#############################################################################
##
#F POL_PreImagesPcsNueK_p_G( gens_K_p, pcgs_nue_K_p )
##
InstallGlobalFunction( POL_PreImagesPcsNueK_p_G ,
function( gens_K_p, pcgs_nue_K_p )
local preImages,i,l1,g,l;
preImages := [];
l1 := pcgs_nue_K_p.trsf;
for l in l1 do
g := gens_K_p[1]^0;
for i in [1..Length(l)] do
g := g*gens_K_p[i]^l[i];
od;
Add( preImages, g );
od;
return preImages;
end );
#############################################################################
##
#F POL_PreImagesPcsI_p_G( pcgs_I_p, gens )
##
InstallGlobalFunction( POL_PreImagesPcsI_p_G , function( pcgs_I_p, gens )
local preImages,m,l,list,k;
preImages := [];
list := pcgs_I_p.wordGens;
for l in list do
k := gens[1]^0;
for m in l do
k := k*gens[m[1]]^m[2];
od;
Add(preImages,k);
od;
return preImages;
end );
#############################################################################
##
#F TestPOL_PreImagesPcsI_p_G( preImgsI_p, p, pcgs_I_p );
##
InstallGlobalFunction( TestPOL_PreImagesPcsI_p_G ,
function( preImgsI_p, p, pcgs_I_p )
local n,i, test;
n := Length( preImgsI_p );
for i in [1..n] do
test := ( preImgsI_p[i]*One(GF(p))
=
pcgs_I_p.gens[n-i+1]);
if not test then
return fail;
fi;
od;
return true;
end );
#############################################################################
##
#F ExponentVector_CPCS_FactorGU_p(pcgs_GU,g)
##
InstallGlobalFunction( ExponentVector_CPCS_FactorGU_p ,
function( pcgs_GU, g )
local h,exp_h,k,l,exp_l,exp,test;
# if G is abelian skip the I_p part
if pcgs_GU.p=0 then
k := g;
exp_h := [];
else
# first we have to compute the part related to preImgs_I_p
# compute the image in I_p
h := g*One(GF(pcgs_GU.p));
exp_h := ExponentvectorPcgs_finite( pcgs_GU.pcgs_I_p, h );
if exp_h = fail then return fail; fi;
# divide off to get the part of g which is in K_p
k := POL_GetPartinK_P( g, exp_h, pcgs_GU.preImgsI_p );
# assert that k is in K_p
Assert( 2, k*One( GF(pcgs_GU.p) ) = ( k*One(GF(pcgs_GU.p)) )^0,
"Failure in ExponentVector_CPCS_FactorGU_p(pcgs_GU,g)\n");
fi;
# now compute the image under nue
l:= POL_InducedActionToSeries( [k], pcgs_GU.radicalSeries );
exp_l:=ExponentVector_AbelianSS( pcgs_GU.pcgs_nue_K_p, l );
if exp_l = fail then return fail; fi;
# merge the exponents
exp:=Concatenation(exp_h,exp_l);
return exp;
end );
#############################################################################
##
#F POL_GetPartinK_P(g,exp_h,preImgsI_p)
##
InstallGlobalFunction( POL_GetPartinK_P, function( g, exp_h, preImgsI_p )
local k,i;
# we know g*K_p = preImgsI_p^exp_h * K_p
k := StructuralCopy(g);
for i in ([1..Length(exp_h)]) do
k := ( preImgsI_p[i]^-exp_h[i] ) * k;
od;
return k;
end );
#############################################################################
##
#F RelativeOrders_CPCS_FactorGU_p( pcgs_GU )
##
InstallGlobalFunction( RelativeOrders_CPCS_FactorGU_p , function( pcgs_GU )
local relOrders_I_p,relOrders_nue_K_p,n,relOrders;
relOrders_I_p := RelativeOrdersPcgs_finite( pcgs_GU.pcgs_I_p );
relOrders_nue_K_p := pcgs_GU.pcgs_nue_K_p.relOrders;
# merge the relOrders
relOrders := Concatenation(relOrders_I_p,relOrders_nue_K_p);
return relOrders;
end );
#############################################################################
##
#F POL_MergeCPCS( pcgs_U_p, pcgs_GU)
##
InstallGlobalFunction( POL_MergeCPCS , function( pcgs_U_p, pcgs_GU )
local pcs,rels1,rels2,rels3,rels;
pcs := Concatenation( pcgs_GU.pcs, pcgs_U_p.pcs );
rels1 := RelativeOrders_CPCS_FactorGU_p( pcgs_GU );
rels2 := pcgs_U_p.rels;
rels:=Concatenation(rels1,rels2);
return rec( pcgs_U_p := pcgs_U_p,
pcgs_GU := pcgs_GU,
pcs := pcs,
rels := rels);
end );
#############################################################################
##
#F ExponentVector_CPCS_PRMGroup( matrix, pcgs )
##
## pcgs is the constructive pcs of a rational polycyclic matrix group
##
InstallGlobalFunction( ExponentVector_CPCS_PRMGroup, function(matrix,pcgs)
local exp1,m1,m2,exp2,exp;
if matrix=matrix^0 then return List( pcgs.rels, x->0 );fi;
# we have G = G/U * U, so matrix = m1 * m2
exp1 := ExponentVector_CPCS_FactorGU_p( pcgs.pcgs_GU, matrix);
if exp1 = fail then return fail; fi;
if Length( exp1 ) = 0 then
#divide off nothing
m2 := matrix;
else
m1 := Exp2Groupelement( pcgs.pcgs_GU.pcs, exp1 );
m2 := (m1^-1)*matrix;
fi;
exp2 := ExponentOfCPCS_Unipotent( m2, pcgs.pcgs_U_p );
if exp2 = fail then return fail; fi;
exp := Concatenation( exp1, exp2);
Assert( 2, Exp2Groupelement( pcgs.pcs, exp) = matrix,
"error in ExponentVector_CPCS_PRMGroup");
return exp;
end );
##############################################################################
##
#F POL_TestIsUnipotenByAbelianGroupByRadSeries( gens, radSers )
##
InstallGlobalFunction( POL_TestIsUnipotenByAbelianGroupByRadSeries,
function( gens, radSers )
local ind,n,i,G;
ind := POL_InducedActionToSeries( gens, radSers );
n := Length( ind );
for i in [1..n] do
G := Group( ind[i] );
if not IsAbelian( G ) then
return false;
fi;
od;
return true;
end );
#############################################################################
##
#E
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2026-03-28
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