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Fix tuple counts for reordered character tables #20

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Merged
shpectorov merged 1 commit into from
Oct 19, 2026
Merged

Fix tuple counts for reordered character tables #20

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10 changes: 6 additions & 4 deletions lib/newgeneratingtuples.gi
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Original file line number Diff line number Diff line change
Expand Up @@ -18,10 +18,12 @@ InstallGlobalFunction(NumberGeneratingTuples,function(group,p,t,g)

full:=[];
sz:=Size(group);
cc:=ConjugacyClasses(group);
# class positions are passed to TotalNumberOfTuples, so they must refer to
# the classes of the character table, whose order may differ from the group's
ct:=CharacterTable(group);
cc:=ConjugacyClasses(ct);
oc:=List(t,s->Filtered([1..Length(cc)],i->s in cc[i]));

ct:=CharacterTable(group);
str:=TotalNumberOfTuples(ct,g,List(oc,c->c[1]));

Add(full,rec(gp:=group,sz:=sz,cc:=cc,oc:=oc,str:=str,pr:=0,nx:=0));
Expand Down Expand Up @@ -55,11 +57,11 @@ InstallGlobalFunction(NumberGeneratingTuples,function(group,p,t,g)
fi;
od;
if not fl then
mcc:=ConjugacyClasses(m);
ct:=CharacterTable(m);
mcc:=ConjugacyClasses(ct);
moc:=List(oc,s-> Union(List(s, n-> Filtered([1..Length(mcc)],i ->
Representative(mcc[i]) in cc[n]))));
if not ([] in moc) then
ct:=CharacterTable(m);
str:=0;
t:=List(tp,c->1);
repeat
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38 changes: 38 additions & 0 deletions tst/ClassOrder.tst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,38 @@
gap> START_TEST("MapClass package: ClassOrder.tst");

# A character table may list the conjugacy classes in another order than
# its group does. Here the group and each subgroup returned by
# MaximalSubgroupClassReps store the identity class last, whereas a character
# table has it first.
gap> IdLast:=function(G)
> local reps,H;
> reps:=List(ConjugacyClasses(G),Representative);
> reps:=Concatenation(reps{[2..Length(reps)]},reps{[1]});
> H:=GroupWithGenerators(GeneratorsOfGroup(G),One(G));
> SetConjugacyClasses(H,List(reps,x->ConjugacyClass(H,x)));
> SetMaximalSubgroupClassReps(H,List(MaximalSubgroupClassReps(G),IdLast));
> return H;
> end;;
gap> G:=IdLast(SymmetricGroup(4));;
gap> ForAll(Concatenation([G],MaximalSubgroupClassReps(G)),
> H->IdentificationOfConjugacyClasses(CharacterTable(H))
> <>[1..NrConjugacyClasses(H)]);
true
gap> t7:=ListWithIdenticalEntries(7,(1,2));;
gap> t8:=ListWithIdenticalEntries(8,(1,2));;
gap> NumberGeneratingTuples(G,[7],t7,0);
0
gap> NumberGeneratingTuples(G,[8],t8,0);
131040
gap> NumberGeneratingTuples(G,[2,2],[(1,2),(1,2),(1,2,3),(1,2,3)],0);
144
gap> NumberGeneratingTuples(G,[1],[(1,2,3)],1);
216
gap> orbs:=GeneratingMCOrbits(G,0,t7:OutputStyle:="silent");;
gap> Length(orbs);
0
gap> orbs:=GeneratingMCOrbits(G,0,[(1,2),(1,2),(1,2,3),(1,2,3)]:
> OutputStyle:="silent");;
gap> List(orbs,o->Length(o.TupleTable));
[ 6 ]
gap> STOP_TEST( "ClassOrder.tst" );
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