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#############################################################################
##
## This file is part of GAP, a system for computational discrete algebra.
## This file's authors include Thomas Breuer, Ansgar Kaup.
##
## Copyright of GAP belongs to its developers, whose names are too numerous
## to list here. Please refer to the COPYRIGHT file for details.
##
## SPDX-License-Identifier: GPL-2.0-or-later
##
## This file contains functions that mainly deal with lattices in the
## context of character tables.
##
#############################################################################
##
#F LLL( <tbl>, <characters>[, <y>][, \"sort\"][, \"linearcomb\"] )
##
InstallGlobalFunction( LLL, function( arg )
local tbl, # character table, first argument
characters, # list of virtual characters, second argument
sorted, # characters sorted by degree
L, # lattice gen. by the virtual characters
i, # loop variable
lllrb, # result of `LLLReducedBasis'
lll, # result
v, # loop over the LLL reduced basis
perm, # permutation arising from sorting characters
y, # optional argument <y>
scpr; # scalar product
# 1. Check the arguments.
if Length( arg ) < 2 or Length( arg ) > 5
or not IsNearlyCharacterTable( arg[1] ) then
Error( "usage: ",
"LLL( <tbl>, <chars> [,<y>][,\"sort\"][,\"linearcomb\"] )" );
fi;
# 2. Get the arguments.
tbl:= arg[1];
characters:= arg[2];
if "sort" in arg then
sorted:= SortedCharacters( tbl, characters, "degree" );
perm:= Sortex( ShallowCopy( sorted ) )
/ Sortex( ShallowCopy( characters ) );
characters:= sorted;
fi;
if IsBound( arg[3] ) and IsRat( arg[3] ) then
y:= arg[3];
else
y:= 3/4;
fi;
# 3. Call the LLL algorithm.
L:= AlgebraByGenerators( Rationals, [ TrivialCharacter( tbl ) ] );
if "linearcomb" in arg then
lllrb:= LLLReducedBasis( L, characters, y, "linearcomb" );
else
lllrb:= LLLReducedBasis( L, characters, y );
fi;
# 4. Make a new result record.
lll:= rec( irreducibles := [],
remainders := [],
norms := [] );
# 5. Sort the relations and transformation if necessary.
if IsBound( lllrb.relations ) then
lll.relations := lllrb.relations;
lll.transformation := lllrb.transformation;
if IsBound( perm ) then
lll.relations := List( lll.relations,
x -> Permuted( x, perm ) );
lll.transformation := List( lll.transformation,
x -> Permuted( x, perm ) );
fi;
fi;
# 6. Add the components used by the character table functions.
lll.irreducibles := [];
lll.remainders := [];
lll.norms := [];
if IsBound( lllrb.transformation ) then
lll.irreddecomp := [];
lll.reddecomp := [];
fi;
for i in [ 1 .. Length( lllrb.basis ) ] do
v:= lllrb.basis[i];
if v[1] < 0 then
v:= AdditiveInverse( v );
if IsBound( lllrb.transformation ) then
lll.transformation[i]:= AdditiveInverse( lll.transformation[i] );
fi;
fi;
scpr:= ScalarProduct( tbl, v, v );
if scpr = 1 then
Add( lll.irreducibles, Character( tbl, v ) );
if IsBound( lllrb.transformation ) then
Add( lll.irreddecomp, lll.transformation[i] );
fi;
else
Add( lll.remainders, VirtualCharacter( tbl, v ) );
Add( lll.norms, scpr );
if IsBound( lllrb.transformation ) then
Add( lll.reddecomp, lll.transformation[i] );
fi;
fi;
od;
if not IsEmpty( lll.irreducibles ) then
Info( InfoCharacterTable, 2,
"LLL: ", Length( lll.irreducibles ), " irreducibles found" );
fi;
# 7. Sort `remainders' and `reddecomp' components if necessary.
if "sort" in arg then
sorted:= SortedCharacters( tbl, lll.remainders, "degree" );
perm:= Sortex( ShallowCopy( lll.remainders ) )
/ Sortex( ShallowCopy( sorted ) );
lll.norms:= Permuted( lll.norms, perm );
lll.remainders:= sorted;
if "linearcomb" in arg then
lll.reddecomp:= Permuted( lll.reddecomp, perm );
fi;
fi;
# 7. Unbind components not used for characters.
Unbind( lll.transformation );
# 8. Return the result.
return lll;
end );
#############################################################################
##
#F Extract( <tbl>, <reducibles>, <gram-matrix> [, <missing> ] )
##
InstallGlobalFunction( Extract, function( arg )
local
# indices
i, j, k, l, n,
# input arrays
tbl, y, gram, missing,
# booleans
deeper, iszero, used, nullbegin, nonmissing,
maxnorm, minnorm, normbound, maxsum, solmat,
f, squares, sfind, choicecollect, sequence,
dependies, solcollect, sum, solcount, max, sumac, kmax,
solution,
# functions
next, zeroset, possiblies, update, correctnorm,
maxsquare, square, ident, begin;
# choosing next vector for combination
next := function( lines, solumat, acidx )
local i, j, solmat, testvec, idxback;
while acidx <= n and k + n - acidx >= kmax do
solmat := List( solumat, ShallowCopy );
if k = 0 then
i := acidx;
while i <= n and not begin( sequence[i] ) do
i := i + 1;
od;
if i > n then
nullbegin := true;
else
nullbegin := false;
if i > acidx then
idxback := sequence[i];
for j in [acidx + 1..1] do
sequence[j] := sequence[j -1];
od;
sequence[acidx] := idxback;
fi;
fi;
fi;
k := k + 1;
f[k] := sequence[acidx];
testvec := [];
for i in [1..k] do
testvec[i] := gram[f[k]][f[i]];
od;
zeroset( solmat, testvec, lines );
acidx := acidx + 1;
possiblies( 1, solmat, testvec, acidx, lines );
k := k - 1;
od;
end;
# filling zero in places that fill already the conditions
zeroset := function( solmat, testvec, lines )
local i, j;
for i in [1..k-1] do
if testvec[i] = 0 then
for j in [1..lines] do
if solmat[j][i] <> 0 and not IsBound( solmat[j][k] ) then
solmat[j][k] := 0;
fi;
od;
fi;
od;
end;
# try and error for the chosen vector
possiblies := function( start, solmat, testvect, acidx, lines )
local i, j, toogreat, equal, solmatback, testvec;
testvec := ShallowCopy( testvect );
toogreat := false;
equal := true;
if k > 1 then
for i in [1..k-1] do
if testvec[i] < 0 then
toogreat := true;
fi;
if testvec[i] <> 0 then
equal := false;
fi;
od;
if testvec[k] < 0 then
toogreat := true;
fi;
else
if not nullbegin then
while start <= gram[f[k]][f[k]] and start < missing do
solmat[start][k] := 1;
start := start + 1;
od;
testvec[k] := 0;
if gram[f[k]][f[k]] > lines then
lines := gram[f[k]][f[k]];
fi;
else
lines := 0;
fi;
fi;
if not equal and not toogreat then
while start < lines and IsBound( solmat[start][k] ) do
start := start + 1;
od;
if start <= lines and not IsBound( solmat[start][k] ) then
solmat[start][k] := 0;
while not toogreat and not equal do
solmat[start][k] := solmat[start][k] + 1;
testvec := update( -1, testvec, start, solmat );
equal := true;
for i in [1..k-1] do
if testvec[i] < 0 then
toogreat := true;
fi;
if testvec[i] <> 0 then
equal := false;
fi;
od;
if testvec[k] < 0 then
toogreat := true;
fi;
od;
fi;
fi;
if equal and not toogreat then
solmatback := List( solmat, ShallowCopy );
for i in [1..missing] do
if not IsBound( solmat[i][k] ) then
solmat[i][k] := 0;
fi;
od;
correctnorm( testvec[k], solmat, lines + 1, testvec[k], acidx, lines );
solmat := solmatback;
#T here was a 'Copy' call. WHY?
fi;
if k > 1 then
while start <= lines and solmat[start][k] > 0 do
solmat[start][k] := solmat[start][k] - 1;
testvec := update( 1, testvec, start, solmat );
solmatback := List( solmat, ShallowCopy );
zeroset( solmat, testvec, lines );
deeper := false;
for i in [1..k-1] do
if solmat[start][i] <> 0 then
deeper := false;
if testvec[i] = 0 then
deeper := true;
else
for j in [1..missing] do
if solmat[j][i] <> 0 and not IsBound(solmat[j][k]) then
deeper := true;
fi;
od;
fi;
fi;
od;
if deeper then
possiblies( start + 1, solmat, testvec, acidx, lines );
fi;
solmat := solmatback;
#T here was a 'Copy' call. WHY?
od;
fi;
end;
# update the remaining conditions to fill
update := function( x, testvec, start, solmat )
local i;
for i in [1..k-1] do
if solmat[start][i] <> 0 then
testvec[i] := testvec[i] + solmat[start][i] * x;
fi;
od;
testvec[k] := testvec[k] - square( solmat[start][k] )
+ square( solmat[start][k] + x );
return testvec;
end;
# correct the norm if all other conditions are filled
correctnorm := function( remainder, solmat, pos, max, acidx, lines )
local i, newsol, ret;
if remainder = 0 and pos <= missing + 1 then
newsol := true;
for i in [1..solcount[k]] do
if ident( solcollect[k][i], solmat ) = missing then
newsol := false;
fi;
od;
if newsol then
if k > kmax then
kmax := k;
fi;
solcount[k] := solcount[k] + 1;
solcollect[k][solcount[k]] := [];
choicecollect[k][solcount[k]] := ShallowCopy( f );
for i in [1..Length( solmat )] do
solcollect[k][solcount[k]][i] := ShallowCopy( solmat[i] );
od;
if k = n and pos = missing + 1 then
ret := 0;
else
ret := max;
if k <> n then
next( lines, solmat, acidx );
fi;
fi;
else
ret := max;
fi;
else
if pos <= missing then
i := maxsquare( remainder, max );
while i > 0 do
solmat[pos][k] := i;
i := correctnorm( remainder-square( i ),
solmat, pos+1, i, acidx, lines + 1);
i := i - 1;
od;
if i < 0 then
ret := 0;
else
ret := max;
fi;
else
ret := 0;
fi;
fi;
return ret;
end;
# compute the maximum squarenumber lower then given integer
maxsquare := function( value, max )
local i;
i := 1;
while square( i ) <= value and i <= max do
i := i + 1;
od;
return i-1;
end;
square := function( i )
if i = 0 then
return( 0 );
else
if not IsBound( squares[i] ) then
squares[i] := i * i;
fi;
return squares[i];
fi;
end;
ident := function( a, b )
# lists the identities of the two given sequences and counts them
local i, j, k, zi, zz, la, lb;
la := Length( a );
lb := Length( b );
zi := [];
zz := 0;
for i in [1..la] do
j := 1;
repeat
if a[i] = b[j] then
k :=1;
while k <= zz and j <> zi[k] do
k := k + 1;
od;
if k > zz then
zz := k;
zi[zz] := j;
j := lb;
fi;
fi;
j := j + 1;
until j > lb;
od;
return( zz );
end;
# looking for character that can stand at the beginning
begin := function( i )
local ind;
if y = [] or gram[i][i] < 4 then
return true;
else
if IsBound( ComputedPowerMaps( tbl )[2] ) then
if ForAll( ComputedPowerMaps( tbl )[2], IsInt ) then
#T ??
ind := AbsInt( Indicator( tbl, [y[i]], 2 )[1]);
if gram[i][i] - 1 <= ind
or ( gram[i][i] = 4 and ind = 1 ) then
return true;
fi;
fi;
fi;
fi;
return false;
end;
# check input parameters
if IsNearlyCharacterTable( arg[1] ) then
tbl := arg[1];
else
Error( "first argument must be character table\n \
usage: Extract( <tbl>, <reducibles>, <gram-matrix> [, <missing>] )" );
fi;
if IsBound( arg[2] ) and IsList( arg[2] ) and IsList( arg[2][1] ) then
y := List( arg[2], ShallowCopy );
else
Error( "second argument must be list of reducible characters\n \
usage: Extract( <tbl>, <reducibles>, <gram-matrix> [, <missing>] )" );
fi;
if IsBound( arg[2] ) and IsList( arg[3] ) and IsList( arg[3][1] ) then
gram := List( arg[3], ShallowCopy );
else
Error( "third argument must be gram-matrix of reducible characters\n \
usage: Extract( <tbl>, <reducibles>, <gram-matrix> [, <missing>] )" );
fi;
n := Length( gram );
if IsBound( arg[4] ) and IsInt( arg[4] ) then
missing := arg[4];
else
missing := n;
nonmissing := true;
fi;
# main program
maxnorm := 0;
minnorm := gram[1][1];
normbound := [];
maxsum := [];
solcollect := [];
choicecollect := [];
sum := [];
solmat := [];
used := [];
solcount := [];
sfind := [];
f := [];
squares := [];
kmax := 0;
for i in [1..missing] do
solmat[i] := [];
od;
for i in [1..n] do
solcount[i] := 0;
used[i] := false;
solcollect[i] := [];
choicecollect[i] := [];
od;
for i in [1..n] do
if gram[i][i] > maxnorm then
maxnorm := gram[i][i];
else
if gram[i][i] < minnorm then
minnorm := gram[i][i];
fi;
fi;
od;
j := 0;
for i in [minnorm..maxnorm] do
k := 1;
while k <= n and gram[k][k] <> i do
k := k + 1;
od;
if k <= n then
j := j + 1;
normbound[j] := rec( norm:=i, first:=k, last:=0 );
if k = n then
normbound[j].last := k;
else
k := n;
while gram[k][k] <> i and k > 0 do
k := k - 1;
od;
if k > 0 then
normbound[j].last := k;
fi;
fi;
fi;
od;
for j in [1..Length( normbound )] do
maxsum[j] := 0;
for i in [normbound[j].first..normbound[j].last] do
if gram[i][i] = normbound[j].norm then
sum[i] := 0;
for k in [1..n] do
sum[i] := sum[i] + gram[i][k];
od;
if sum[i] > maxsum[j] then
maxsum[j] := sum[i];
fi;
fi;
od;
od;
k := 1;
sequence := [];
i:= 1;
while i <= Length( normbound ) do
max := maxsum[i];
sumac := 0;
for j in [normbound[i].first..normbound[i].last] do
if gram[j][j] = normbound[i].norm and sum[j] > sumac
and sum[j] <= max and not used[j] then
sequence[k] := j;
sumac := sum[j];
fi;
od;
if IsBound( sequence[k] ) then
max := sumac;
used[sequence[k]] := true;
k := k + 1;
else
i := i + 1;
fi;
od;
k := 0;
next( 1, solmat, 1 );
solution := rec( solution := [], choice := choicecollect[kmax] );
for i in [1..solcount[kmax]] do
solution.solution[i] := [];
l := 0;
for j in [1..missing] do
iszero := true;
for k in [1..kmax] do
if solcollect[kmax][i][j][k] <> 0 then
iszero := false;
fi;
od;
if not iszero then
l := l + 1;
solution.solution[i][l] := solcollect[kmax][i][j];
fi;
od;
od;
return( solution );
end );
#############################################################################
##
#F Decreased( <tbl>, <chars>, <decompmat>, [ <choice> ] )
##
InstallGlobalFunction( Decreased, function( arg )
local
# indices
m, n, n1, i, i1, i2, i3, i4, j, jj, j1, j2, j3,
# booleans
ende1, ende2, ok, change, delline, delcolumn,
# help fields
deleted, kgv, l1, l2, l3, dim, ident,
# matrices
invmat, remmat, remmat2, solmat, nonzero,
# double-indices
columnidx, lineidx, system, components, compo2,
# output-fields
sol, red, redcount, irred,
# help fields
IRS, SFI, lc, nc, char, char1, entries,
# input fields
tbl, y, choice,
# functions
Idxset, Identset, Invadd, Invmult, Nonzeroset;
Idxset := function()
# update indices
local i1, j1, m1;
i1 := 0;
for i in [1..m] do
if not delline[i] then
i1 := i1 + 1;
lineidx[i1] := i;
fi;
od;
m1 := i1;
j1 := 0;
for j in [1..n] do
if not delcolumn[j] then
j1 := j1 + 1;
columnidx[j1] := j;
fi;
od;
n1 := j1;
end;
Identset := function( veca, vecb )
#T just one place where this is called ...
# count identities of veca and vecb and store "non-identities"
local la, lb, i, j, n, nonid, nic, r;
n := 0;
la := Length( veca );
lb := Length( vecb );
j := 1;
nonid := [];
nic := 0;
for i in [1..la] do
while j <= lb and veca[i] > vecb[j] do
nic := nic + 1;
nonid[nic] := vecb[j];
j := j + 1;
od;
if j <= lb and veca[i] = vecb[j] then
n := n + 1;
j := j + 1;
fi;
od;
while j <= lb do
nic := nic + 1;
nonid[nic] := vecb[j];
j := j + 1;
od;
r := rec( nonid := nonid, id := n );
return( r );
end;
Invadd := function( j1, j2, l )
# addition of two lines of invmat
local i;
for i in [1..n] do
if invmat[i][j2] <> 0 then
invmat[i][j1] := invmat[i][j1] - l * invmat[i][j2];
fi;
od;
end;
Invmult := function( j1, l )
# multiply line of invmat
local i;
if l <> 1 then
for i in [1..n] do
if invmat[i][j1] <> 0 then
invmat[i][j1] := invmat[i][j1] * l;
fi;
od;
fi;
end;
Nonzeroset := function( j )
# entries <> 0 in j-th column of 'solmat'
local i, j1;
nonzero[j] := [];
j1 := 0;
for i in [1..m] do
if solmat[i][j] <> 0 then
j1 := j1 + 1;
nonzero[j][j1] := i;
fi;
od;
entries[j] := j1;
end;
# check input parameters
if Length( arg ) < 3 or Length( arg ) > 4 then
Error( "usage: Decreased( <tbl>, <list of char>,\n",
"<decomposition matrix>, [<choice>] )" );
fi;
if IsNearlyCharacterTable( arg[1] ) then
tbl := arg[1];
else
Error( "first argument must be a nearly character table\n",
"usage: Decreased( <tbl>, <list of char>,\n",
"<decomposition matrix>, [<choice>] )" );
fi;
if IsList( arg[2] ) and IsList( arg[2][1] ) then
y := arg[2];
else
Error( "second argument must be list of characters\n",
"usage: Decreased( <tbl>, <list of char>,\n",
"<decomposition matrix>, [<choice>] )" );
fi;
if IsList( arg[3] ) and IsList( arg[3][1] ) then
solmat := List( arg[3], ShallowCopy );
else
Error( "third argument must be decomposition matrix\n",
"usage: Decreased( <tbl>, <list of char>,\n",
"<decomposition-matrix>, [<choice>] )" );
fi;
if not IsBound( arg[4] ) then
choice := [ 1 .. Length( y ) ];
elif IsList( arg[4] ) then
choice := arg[4];
else
Error( "forth argument contains choice of characters\n",
"usage: Decreased( <tbl>, <list of char>,\n",
"<decomposition-matrix>, [<choice>] )" );
fi;
# initialisations
lc := Length( y[1] );
nc := [];
for i in [1..lc] do
nc[i] := 0;
od;
columnidx := [];
lineidx := [];
nonzero := [];
entries := [];
delline := [];
delcolumn := [];
# number of lines
m := Length( solmat );
# number of columns
n := Length( solmat[1] );
invmat := IdentityMat( n );
for i in [1..m] do
delline[i] := false;
od;
for j in [1..n] do
delcolumn[j] := false;
od;
i := 1;
# check lines for information
while i <= m do
if not delline[i] then
entries[i] := 0;
for j in [1..n] do
if solmat[i][j] <> 0 and not delcolumn[j] then
entries[i] := entries[i] + 1;
if entries[i] = 1 then
nonzero[i] := j;
fi;
fi;
od;
if entries[i] = 1 then
delcolumn[nonzero[i]] := true;
delline[i] := true;
j := 1;
while j < i and solmat[j][nonzero[i]] = 0 do
j := j + 1;
od;
if j < i then
i := j;
else
i := i + 1;
fi;
else
if entries[i] = 0 then
delline[i] := true;
fi;
i := i + 1;
fi;
else
i := i + 1;
fi;
od;
Idxset();
deleted := m - Length(lineidx);
for j in [1..n] do
Nonzeroset( j );
od;
ende1 := false;
while not ende1 and deleted < m do
j := 1;
# check solo-entry-columns
while j <= n do
if entries[j] = 1 then
change := false;
for jj in [1..n] do
if (delcolumn[j] and delcolumn[jj])
or not delcolumn[j] then
if solmat[nonzero[j][1]][jj] <> 0 and jj <> j then
change := true;
kgv := Lcm( solmat[nonzero[j][1]][j],
solmat[nonzero[j][1]][jj] );
l1 := kgv / solmat[nonzero[j][1]][jj];
Invmult( jj, l1 );
for i1 in [1..Length( nonzero[jj] )] do
solmat[nonzero[jj][i1]][jj]
:= solmat[nonzero[jj][i1]][jj] * l1;
od;
Invadd( jj, j, kgv/solmat[nonzero[j][1]][j] );
solmat[nonzero[j][1]][jj] := 0;
Nonzeroset( jj );
fi;
fi;
od;
if not delline[nonzero[j][1]] then
delline[nonzero[j][1]] := true;
delcolumn[j] := true;
deleted := deleted + 1;
Idxset();
fi;
if change then
j := 1;
else
j := j + 1;
fi;
else
j := j + 1;
fi;
od;
# search for Equality-System
# system : chosen columns
# components : entries <> 0 in the chosen columns
dim := 2;
change := false;
ende2 := false;
while dim <= n1 and not ende2 do
j3 := 1;
while j3 <= n1 and not ende2 do
j2 := j3;
j1 := 0;
system := [];
components := [];
while j2 <= n1 do
while j2 <= n1 and entries[columnidx[j2]] > dim do
j2 := j2 + 1;
od;
if j2 <= n1 then
if j1 = 0 then
j1 := 1;
system[j1] := columnidx[j2];
components := ShallowCopy( nonzero[columnidx[j2]] );
else
ident := Identset( components, nonzero[columnidx[j2]] );
if dim - Length( components ) >= entries[columnidx[j2]]
- ident.id then
j1 := j1 + 1;
system[j1] := columnidx[j2];
if ident.id < entries[columnidx[j2]] then
compo2 := ShallowCopy( components );
components := [];
i1 := 1;
i2 := 1;
i3 := 1;
# append new entries to "components"
while i1 <= Length( ident.nonid )
or i2 <= Length( compo2 ) do
if i1 <= Length( ident.nonid ) then
if i2 <= Length( compo2 ) then
if ident.nonid[i1] < compo2[i2] then
components[i3] := ident.nonid[i1];
i1 := i1 + 1;
else
components[i3] := compo2[i2];
i2 := i2 + 1;
fi;
else
components[i3] := ident.nonid[i1];
i1 := i1 + 1;
fi;
else
if i2 <= Length( compo2 ) then
components[i3] := compo2[i2];
i2 := i2 + 1;
fi;
fi;
i3 := i3 + 1;
od;
fi;
fi;
fi;
j2 := j2 + 1;
fi;
od;
# try to solve system with Gauss
if Length( system ) > 1 then
for i1 in [1..Length( components )] do
i2 := 1;
repeat
ok := true;
if solmat[components[i1]][system[i2]] = 0 then
ok := false;
else
for i3 in [1..i1-1] do
if solmat[components[i3]][system[i2]] <> 0 then
ok := false;
fi;
od;
fi;
if not ok then
i2 := i2 + 1;
fi;
until ok or i2 > Length( system );
if ok then
for i3 in [1..Length( system )] do
if i3 <> i2
and solmat[components[i1]][system[i3]] <> 0 then
change := true;
kgv := Lcm( solmat[components[i1]][system[i3]],
solmat[components[i1]][system[i2]] );
l2 := kgv / solmat[components[i1]][system[i2]];
l3 := kgv / solmat[components[i1]][system[i3]];
for i4 in [1..Length( nonzero[system[i3]] )] do
solmat[nonzero[system[i3]][i4]][system[i3]]
:= solmat[nonzero[system[i3]][i4]][system[i3]]*l3;
od;
Invmult( system[i3], l3 );
for i4 in [1..Length( nonzero[system[i2]] )] do
solmat[nonzero[system[i2]][i4]][system[i3]]
:= solmat[nonzero[system[i2]][i4]][system[i3]]
- solmat[nonzero[system[i2]][i4]][system[i2]]*l2;
od;
Invadd( system[i3], system[i2], l2 );
Nonzeroset( system[i3] );
if entries[system[i3]] = 0 then
delcolumn[system[i3]] := true;
Idxset();
fi;
fi;
od;
fi;
od;
# check for columns with only one entry <> 0
for i1 in [1..Length( system )] do
if entries[system[i1]] = 1 then
ende2 := true;
fi;
od;
if not ende2 then
j3 := j3 + 1;
fi;
else
j3 := j3 + 1;
fi;
od;
dim := dim + 1;
od;
if dim > n1 and not change and j3 > n1 then
ende1 := true;
fi;
od;
# check, if
# the transformation of solmat allows computation of new irreducibles
remmat := [];
for i in [1..m] do
remmat[i] := [];
delline[i] := true;
od;
redcount := 0;
red := [];
irred := [];
j := 1;
sol := true;
while j <= n and sol do
# computation of character
char := ShallowCopy( nc );
for i in [1..n] do
if invmat[i][j] <> 0 then
char := char + invmat[i][j] * y[choice[i]];
fi;
od;
# probably irreducible ==> has to pass tests
if entries[j] = 1 then
if solmat[nonzero[j][1]][j] <> 1 then
char1 := char/solmat[nonzero[j][1]][j];
else
char1 := char;
fi;
if char1[1] < 0 then
char1 := - char1;
fi;
# is 'char1' real?
IRS := ForAll( char1, x -> GaloisCyc(x,-1) = x );
# Frobenius Schur indicator
if IsBound( ComputedPowerMaps( tbl )[2] )
and ForAll( ComputedPowerMaps( tbl )[2], IsInt ) then
#T ??
SFI:= Indicator( tbl, [ char1 ], 2 )[1];
else
SFI:= Unknown();
Info( InfoCharacterTable, 2,
"Decreased: 2nd power map not available or not unique,\n",
"#I no test with 'Indicator'" );
fi;
# test if 'char1' can be an irreducible character
if char1[1] = 0
or ForAny( char1, x -> not IsCycInt(x) )
or ScalarProduct( tbl, char1, char1 ) <> 1
or ( IsCyc( SFI ) and ( ( IRS and AbsInt( SFI ) <> 1 ) or
( not IRS and SFI <> 0 ) ) ) then
Info( InfoCharacterTable, 2,
"Decreased : computation of ",
Ordinal( Length( irred ) + 1 ), " character failed" );
return fail;
else
# irreducible character found
Add( irred, Character( tbl, char1 ) );
fi;
else
# what a pity (!), some reducible character remaining
if char[1] < 0 then
char := - char;
fi;
if char <> nc then
redcount := redcount + 1;
red[redcount] := ClassFunction( tbl, char );
for i in [1..m] do
remmat[i][redcount] := solmat[i][j];
if solmat[i][j] <> 0 then
delline[i] := false;
fi;
od;
fi;
fi;
j := j+1;
od;
i1 := 0;
remmat2 := [];
for i in [1..m] do
if not delline[i] then
i1 := i1 + 1;
remmat2[i1] := remmat[i];
fi;
od;
return rec( irreducibles := irred,
remainders := red,
matrix := remmat2 );
end );
#############################################################################
##
#F OrthogonalEmbeddingsSpecialDimension( <tbl>, <reducibles>, <grammat>,
#F [, \"positive\"], <dim> )
##
InstallGlobalFunction( OrthogonalEmbeddingsSpecialDimension, function ( arg )
local red, dim, reducibles, tbl, emb, dec, i, s, irred;
# check input
if Length( arg ) < 4 then
Error( "please specify desired dimension\n",
"usage : OrthogonalE...( <tbl>, <reducibles>,\n",
"<gram-matrix>[, \"positive\" ], <dim> )" );
fi;
if IsInt( arg[4] ) then
dim := arg[4];
else
if IsBound( arg[5] ) then
if IsInt( arg[5] ) then
dim := arg[5];
else
Error( "please specify desired dimension\n",
"usage : Orthog...( <tbl>, < reducibles >,\n",
"< gram-matrix >, [, <\"positive\"> ], < integer > )" );
fi;
fi;
fi;
tbl := arg[1];
reducibles := arg[2];
if Length( arg ) = 4 then
emb := OrthogonalEmbeddings( arg[3], arg[4] );
else
emb := OrthogonalEmbeddings( arg[3], arg[4], arg[5] );
fi;
s := [];
for i in [1..Length(emb.solutions)] do
if Length( emb.solutions[i] ) = dim then
Add( s, emb.vectors{ emb.solutions[i] } );
fi;
od;
dec:= List( s, x -> Decreased( tbl, reducibles, x ) );
dec:= Filtered( dec, x -> x <> fail );
if dec = [] then
Info( InfoCharacterTable, 2,
"OrthogonalE...: no embedding corresp. to characters" );
return rec( irreducibles:= [], remainders:= reducibles );
fi;
irred:= Set( dec[1].irreducibles );
for i in [2..Length(dec)] do
IntersectSet( irred, dec[i].irreducibles );
od;
red:= ReducedClassFunctions( tbl, irred, reducibles );
Append( irred, red.irreducibles );
return rec( irreducibles:= irred, remainders:= red.remainders );
end );
#############################################################################
##
#F DnLattice( <tbl>, <g1>, <y1> )
##
InstallGlobalFunction( DnLattice, function( tbl, g1, y1 )
local
# indices
i, i1, j, j1, k, k1, l, next,
# booleans
empty, change, used, addable, SFIbool,
# dimensions
n,
# help fields
found, foundpos,
z, nullcount, nullgenerate,
maxentry, max, ind, irred, irredcount, red,
blockcount, blocks, perm, addtest, preirred,
# Gram matrix
g, gblock,
# characters
y, y2,
# variables for recursion
root, rootcount, solution, ligants, ligantscount, begin,
depth, choice, ende, sol,
# functions
callreduced, nullset, maxset, Search, Add, DnSearch, test;
# counts zeroes in given line
nullset := function( g, i )
local j;
nullcount[ i ] := 0;
for j in [ 1..n ] do
if g[ j ] = 0 then
nullcount[ i ] := nullcount[ i ] + 1;
fi;
od;
end;
# searches line with most non-zero-entries
maxset := function( )
local i;
maxentry := 1;
max := n;
for i in [ 1..n ] do
if nullcount[ i ] < max then
max := nullcount[ i ];
maxentry := i;
fi;
od;
end;
# searches lines to add in order to produce zeroes
Search := function( j )
nullgenerate := 0;
if g[ j ][ maxentry ] > 0 then
for k in [ 1..n ] do
if k <> maxentry and k <> j then
if g[ maxentry ][ k ] <> 0 then
if g[ j ][ k ] = g[ maxentry ][ k ] then
nullgenerate := nullgenerate + 1;
else
nullgenerate := nullgenerate - 1;
fi;
fi;
fi;
od;
else
if g[ j ][ maxentry ] < 0 then
for k in [ 1..n ] do
if k <> maxentry and k <> j then
if g[ maxentry ][ k ] <> 0 then
if g[ j ][ k ] = -g[ maxentry ][ k ] then
nullgenerate := nullgenerate + 1;
else
nullgenerate := nullgenerate - 1;
fi;
fi;
fi;
od;
fi;
fi;
if nullgenerate > 0 then
change := true;
Add( j, maxentry );
j := j + 1;
fi;
end;
# adds two lines/columns
Add := function( i, j )
local k;
y[ i ] := y[ i ] - g[ i ][ j ] * y[ j ];
g[ i ] := g[ i ] - g[ i ][ j ] * g[ j ];
for k in [ 1..i-1 ] do
g[ k ][ i ] := g[ i ][ k ];
od;
g[ i ][ i ] := 2;
for k in [ i+1..n ] do
g[ k ][ i ] := g[ i ][ k ];
od;
end;
# backtrack-search for dn-lattice
DnSearch := function( begin, depth, oldchoice )
local connections, connect, i1, j1, choice, found;
choice := ShallowCopy( oldchoice );
if depth = 3 then
# d4-lattice found !!!
solution := 1;
ende := true;
if n > 4 then
i1 := 0;
found := false;
while not found and i1 < n do
i1 := i1 + 1;
if i1 <> root[ j ] and i1 <> choice[ 1 ]
and i1 <> choice[ 2 ] and i1 <> choice[ 3 ] then
connections := 0;
for j1 in [1..3] do
if gblock[ i1 ][ choice[ j1 ] ] <> 0 then
connections := connections + 1;
connect := choice[ j1 ];
fi;
od;
if connections = 1 then
found := true;
choice[ 4 ] := connect;
solution := solution + 1;
fi;
fi;
i1 := i1 + 1;
od;
fi;
sol := choice;
else
i1 := begin;
while not ende and i1 <= ligantscount do
found := true;
for j1 in [1..depth] do
if gblock[ ligants[ i1 ] ][ choice[ j1 ] ] <> 0 then
found := false;
fi;
od;
if found then
depth := depth + 1;
choice[ depth ] := ligants[ i1 ];
DnSearch( i1 + 1, depth, choice );
depth := depth - 1;
else
i1 := i1 + 1;
fi;
if ligantscount - i1 + 1 + depth < 3 then
ende := true;
fi;
od;
fi;
end;
test := function(z)
# some tests for the found characters
local result, IRS, SFI, i1, y1, ind, testchar;
testchar := z/2;
result := true;
IRS := ForAll( testchar, x -> GaloisCyc(x,-1) = x );
if IsBound( ComputedPowerMaps( tbl )[2] ) then
if ForAll( ComputedPowerMaps( tbl )[2], IsInt ) then
SFI := Indicator( tbl, [testchar], 2 )[1];
SFIbool := true;
else
Info( InfoCharacterTable, 2,
"DnLattice: 2nd power map not available or not unique,\n",
"#I cannot test with Indicator" );
SFIbool := false;
fi;
else
Info( InfoCharacterTable, 2,
"DnLattice: 2nd power map not available\n",
"#I cannot test with Indicator" );
SFIbool := false;
fi;
if SFIbool then
if ForAny( testchar, x -> IsRat(x) and not IsInt(x) )
or ScalarProduct( tbl, testchar, testchar ) <> 1
or testchar[1] = 0
or ( IRS and AbsInt( SFI ) <> 1 )
or ( not IRS and SFI <> 0 ) then
result := false;
fi;
else
if ForAny( testchar, x -> IsRat(x) and not IsInt(x) )
or ScalarProduct( tbl, testchar, testchar ) <> 1
or testchar[1] = 0 then
result := false;
fi;
fi;
return result;
end;
# reduce whole lattice with the found irreducible
callreduced := function()
z[ 1 ] := z[ 1 ]/ 2 ;
if ScalarProduct( tbl, z[ 1 ], z[ 1 ] ) = 1 then
irredcount := irredcount + 1;
if z[ 1 ][ 1 ] > 0 then
irred[ irredcount ] := Character( tbl, z[ 1 ] );
else
irred[ irredcount ] := Character( tbl, -z[ 1 ] );
fi;
y1 := y{ [ blocks.begin[i] .. blocks.ende[i] ] };
red := ReducedClassFunctions( tbl, z, y1 );
Append( irred, List( red.irreducibles, x -> Character( tbl, x ) ) );
irredcount := Length( irred );
y2 := Concatenation( y2, red.remainders );
fi;
end;
# check input parameters
if not IsNearlyCharacterTable( tbl ) then
Error( "first argument must be a nearly character table\n",
"usage: DnLattice( <tbl>, <gram-matrix>, <reducibles> )" );
fi;
empty := false;
if not IsEmpty( g1 ) then
if IsList( g1 ) and IsBound( g1[1] ) and IsList( g1[1] ) then
g := List( g1, ShallowCopy );
else
Error( "second argument must be Gram matrix of characters\n",
"usage: DnLattice( <tbl>, <gram-matrix>, <reducibles> )" );
fi;
else
empty := true;
fi;
if not IsEmpty( y1 ) then
if IsList( y1 ) and IsBound( y1[1] ) and IsList( y1[1] ) then
y := List( y1, ShallowCopy );
else
Error( "third argument must be list of reducible characters\n",
"usage: DnLattice( <tbl>, <gram-matrix>, <reducibles> )" );
fi;
else
empty := true;
fi;
y2 := [ ];
irred := [ ];
if not empty then
n := Length( y );
for i in [1..n] do
if g[i][i] <> 2 then
Error( "reducible characters don't have norm 2\n",
"usage: DnLattice( <tbl>, <gram-matrix>, <reducibles> )" );
fi;
od;
# initialisations
z := [ ];
used := [ ];
next := [ ];
nullcount := [ ];
for i in [1..n] do
used[i] := false;
od;
blocks := rec( begin := [ ], ende := [ ] );
blockcount := 0;
irredcount := 0;
change := true;
while change do
change := false;
for i in [ 1..n ] do
nullset( g[ i ], i );
od;
maxset( );
while max < n-2 and not change do
while maxentry <= n and not change do
if nullcount[ maxentry ] <> max then
maxentry := maxentry + 1;
else
j := 1;
while j < maxentry and not change do
Search( j );
j := j + 1;
od;
j := maxentry + 1;
while j <= n and not change do
Search( j );
j := j + 1;
od;
if not change then
maxentry := maxentry + 1;
fi;
fi;
od;
if not change then
max := max + 1;
maxentry := 1;
fi;
od;
# 2 step-search in order to produce zeroes
# 2_0_Box-Method
change := false;
i := 1;
while i <= n and not change do
while i <= n and nullcount[ i ] > n-3 do
i := i + 1;
od;
if i <= n then
j := 1;
while j <= n and not change do
while j <= n and g[ i ][ j ] <> 0 do
j := j + 1;
od;
if j <= n then
i1 := 1;
while i1 <= n and not change do
while i1 <= n
and ( i1 = i or i1 = j or g[ i1 ][ j ] = 0 ) do
i1 := i1 + 1;
od;
if i1 <= n then
addtest := g[ i ] - g[ i ][ i1 ] * g[ i1 ];
nullgenerate := 0;
addable := true;
for k in [ 1..n ] do
if addtest[ k ] = 0 then
nullgenerate := nullgenerate + 1;
else
if AbsInt( addtest[ k ] ) > 1 then
addable := false;
fi;
fi;
od;
if addable then
nullgenerate := nullgenerate - nullcount[ i ];
for k in [ 1..n ] do
if k <> i and k <> j then
if addtest[ k ]
= addtest[ j ] * g[ j ][ k ] then
if g[ j ][ k ] <> 0 then
nullgenerate := nullgenerate + 1;
fi;
else
if addtest[ k ] <> 0 then
if g[ j ][ k ] = 0 then
nullgenerate := nullgenerate - 1;
else
addable := false;
fi;
fi;
fi;
fi;
od;
if nullgenerate > 0 and addable then
Add( i, i1 );
Add( j, i );
change := true;
fi;
fi;
i1 := i1 + 1;
fi;
od;
j := j + 1;
fi;
od;
i := i + 1;
fi;
od;
od;
i := 1;
j := 0;
next[ 1 ] := 1;
while j < n do
blockcount := blockcount + 1;
blocks.begin[ blockcount ] := i;
l := 0;
used[ next [ i ] ] := true;
j := j + 1;
y2[ j ] := y[ next [ i ] ];
while l >= 0 do
for k in [ 1..n ] do
if g[ next[ i ] ][ k ] <> 0 and not used[ k ] then
l := l + 1;
next[ i + l ] := k;
j := j + 1;
y2[ j ] := y[ k ];
used[ k ] := true;
fi;
od;
i := i + 1;
l := l - 1;
od;
blocks.ende[ blockcount ] := i - 1;
k := 1;
while k <= n and used[ k ] do
k := k + 1;
od;
if k <= n then
next[i] := k;
fi;
od;
perm := PermList( next )^-1;
for i in [1..n] do
g[i] := Permuted( g[i], perm );
od;
g := Permuted( g, perm );
y := y2;
y2 := [ ];
# search for d4/d5 - lattice
for i in [1..blockcount] do
n := blocks.ende[ i ] - blocks.begin[ i ] + 1;
solution := 0;
if n >= 4 then
gblock := [ ];
j1 := 0;
for j in [ blocks.begin[ i ]..blocks.ende[ i ] ] do
j1 := j1 + 1;
gblock[ j1 ] := [ ];
k1 := 0;
for k in [ blocks.begin[ i ]..blocks.ende[ i ] ] do
k1 := k1 + 1;
gblock[ j1 ][ k1 ] := g[ j ][ k ];
od;
od;
root := [ ];
rootcount := 0;
for j in [1..n] do
nullset( gblock[ j ], j );
if nullcount[ j ] < n - 3 then
rootcount := rootcount + 1;
root[ rootcount ] := j;
fi;
od;
j := 1;
while solution = 0 and j <= rootcount do
ligants := [ ];
ligantscount := 0;
for k in [1..n] do
if k <> root[ j ] and gblock[ root[ j ] ][ k ] <> 0 then
ligantscount := ligantscount + 1;
ligants[ ligantscount ] := k;
fi;
od;
begin := 1;
depth := 0;
choice := [ ];
ende := false;
DnSearch( begin, depth, choice );
if solution > 0 then
choice := sol;
fi;
j := j + 1;
od;
fi;
# test of the found irreducibles
if solution = 1 then
# treatment of D4-lattice
found := 0;
preirred := y{ [ blocks.begin[i] .. blocks.ende[i] ] };
z[1] := preirred[choice[1]] + preirred[choice[2]];
if test(z[1]) then
red := ReducedClassFunctions( tbl, preirred, [ z[1] ] );
if ForAll( red.irreducibles, test ) then
found := found + 1;
foundpos := 1;
fi;
fi;
z[2] := preirred[choice[1]] + preirred[choice[3]];
if test(z[2]) then
red := ReducedClassFunctions( tbl, preirred, [ z[2] ] );
if ForAll( red.irreducibles, test ) then
found := found + 1;
foundpos := 2;
fi;
fi;
z[3] := preirred[choice[2]] + preirred[choice[3]];
if test(z[3]) then
red := ReducedClassFunctions( tbl, preirred, [ z[3] ] );
if ForAll( red.irreducibles, test ) then
found := found + 1;
foundpos := 3;
fi;
fi;
if found = 1 then
z := [z[foundpos]];
callreduced();
fi;
else
# treatment of D5-lattice
if solution = 2 then
if choice [ 1 ] <> choice [ 4 ] then
z[ 1 ] := y[ blocks.begin[ i ] + choice[ 1 ] - 1 ];
if choice [ 2 ] <> choice [ 4 ] then
z[ 1 ]
:= z[ 1 ] + y[ blocks.begin[ i ] + choice[ 2 ] - 1 ];
else
z[ 1 ]
:= z[ 1 ] + y[ blocks.begin[ i ] + choice[ 3 ] - 1 ];
fi;
else
z[ 1 ] := y[ blocks.begin[ i ] + choice[ 2 ] - 1 ]
+ y[ blocks.begin[ i ] + choice[ 3 ] - 1 ];
fi;
found := 0;
if test(z[1]) then
callreduced();
fi;
else
Append( y2, y{ [ blocks.begin[i] .. blocks.ende[i] ] } );
fi;
fi;
od;
if irredcount > 0 then
g := MatScalarProducts( tbl, y2, y2 );
fi;
else
# input was empty i.e. empty=true
g := [];
fi;
return rec( gram:=g, remainders:=y2, irreducibles:=irred );
end );
#############################################################################
##
#F DnLatticeIterative( <tbl>, <red> )
##
InstallGlobalFunction( DnLatticeIterative, function( tbl, red )
local dnlat, red1, norms, i, reduc, irred, norm2, g;
# check input parameters
if not IsNearlyCharacterTable( tbl ) then
Error( "first argument must be a nearly character table\n",
"usage: DnLatticeIterative( <tbl>, <record or list> )" );
fi;
if not IsRecord( red ) and not IsList( red ) then
Error( "second argument must be record or list\n",
"usage: DnLatticeIterative( <tbl>, <record or list> )" );
fi;
if IsRecord( red ) and not IsBound( red.remainders ) then
Error( "second record must contain a field 'remainders'\n",
"usage: DnLatticeIterative( <tbl>, <record or list> )" );
fi;
if not IsRecord( red ) then
red := rec( remainders:=red );
fi;
if not IsBound( red.norms ) then
norms := List( red.remainders, x -> ScalarProduct( tbl, x, x ) );
else
norms := ShallowCopy( red.norms );
fi;
reduc := List( red.remainders, ShallowCopy );
irred := [];
repeat
norm2 := [];
for i in [1..Length( reduc )] do
if norms[i] = 2 then
Add( norm2, reduc[i] );
fi;
od;
g := MatScalarProducts( tbl, norm2, norm2 );
dnlat := DnLattice( tbl, g, norm2 );
Append( irred, dnlat.irreducibles );
red1:= ReducedClassFunctions( tbl, dnlat.irreducibles, reduc );
reduc := red1.remainders;
Append( irred, red1.irreducibles );
norms:= List( reduc, x -> ScalarProduct( tbl, x, x ) );
until dnlat.irreducibles=[] and red1.irreducibles=[];
return rec( irreducibles:=irred, remainders:=reduc , norms := norms );
end );
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