Skip to content

Fix several regressions introduced by #6494 #6510

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
fingolfin merged 4 commits into from
Aug 15, 2026
+37 −13
Merged

Fix several regressions introduced by #6494 #6510

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
4 commits
Select commit Hold shift + click to select a range
33fc5ac
FIX remaining #6494 bug
hulpke Aug 14, 2026
eba1c45
Fix another error
fingolfin Aug 15, 2026
a6ca8bc
cleanup
fingolfin Aug 15, 2026
d7955d5
Add regression tests
fingolfin Aug 15, 2026
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
27 changes: 14 additions & 13 deletions lib/grppcext.gi
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -370,12 +370,12 @@ local ag, p1iso, agp, p2iso, DP, p1, p2, gens, genimgs, triso,s,i,u,opt,

# are both groups solvable?
p2iso:=IsomorphismPermGroup(DirectProductInfo(D).groups[2]);
gp2:=ImagesSource(p2iso);
gp2:=Image(p2iso,DirectProductInfo(D).groups[2]);
Comment thread
fingolfin marked this conversation as resolved.
if IsSolvableGroup(gp2) and IsSolvableGroup(agp) then
# both groups are solvable -- go solvable
pc1:=IsomorphismPcGroup(agp);
pc2:=IsomorphismPcGroup(gp2);
DP:=DirectProduct(ImagesSource(pc1),ImagesSource(pc2));
DP:=DirectProduct(Image(pc1,agp),Image(pc2,gp2));
Comment thread
fingolfin marked this conversation as resolved.
p1:=Projection(DP,1);
p2:=Projection(DP,2);
gens:=Pcgs(DP);
Expand Down Expand Up @@ -528,7 +528,6 @@ local G, M, Mgrp, oper, A, B, D, translate, gens, genimgs, triso, K, K1,
if A=fail and Length(arg)=2 then
# search through automorphism group for projection image and reps,
# then add module automorphisms
gens:=GeneratorsOfGroup(G);
if A=fail then
Info( InfoCompPairs, 1, " CompP: compute aut group");
A:=AutomorphismGroup(G);
Expand All @@ -538,22 +537,22 @@ local G, M, Mgrp, oper, A, B, D, translate, gens, genimgs, triso, K, K1,
direct:=true;
fi;

elif A=fail and Length(arg)=3 and HasDirectProductInfo(arg[3])
and IsGroupOfAutomorphismsFiniteGroup(Image(Projection(arg[3],1))) then
elif A=fail and Length(arg)=3 and HasDirectProductInfo(arg[3]) then

A:=Image(Projection(arg[3],1));
B:=Image(Projection(arg[3],2));
u:=B;
gens:=GeneratorsOfGroup(G);
if Size(A)>1 and Size(B)>1 and Size(A)*Size(B)>1000 then
A:=DirectProductInfo(arg[3]).groups[1];
B:=DirectProductInfo(arg[3]).groups[2];

if IsGroupOfAutomorphismsFiniteGroup(A) and Size(A)>1 and Size(B)>1 and Size(A)*Size(B)>1000 then
direct:=true;
u:=B;
else
A:=fail;
fi;

elif IsPcgs(Ggens) and Length(Ggens)=Length(M.generators) then
oper := GroupHomomorphismByImagesNC( G, Mgrp, Ggens, M.generators );
fi;

if direct then
gens:=GeneratorsOfGroup(G);
triso:=NiceMonomorphism(A:autactbase:=fail);
if not IsPermGroup(Image(triso)) then
triso:=IsomorphismPermGroup(A:autactbase:=fail);
Expand Down Expand Up @@ -586,7 +585,7 @@ local G, M, Mgrp, oper, A, B, D, translate, gens, genimgs, triso, K, K1,
B:=Difference(B,[i]);
fi;
od;
K:=Group(GeneratorsOfGroup(K){B});
K:=Group(GeneratorsOfGroup(K){B}, One(K));
pool:=pool{B};

B:=MTX.ModuleAutomorphisms(M);
Expand Down Expand Up @@ -616,6 +615,8 @@ local G, M, Mgrp, oper, A, B, D, translate, gens, genimgs, triso, K, K1,
return A;
fi;

elif IsPcgs(Ggens) and Length(Ggens)=Length(M.generators) then
oper := GroupHomomorphismByImagesNC( G, Mgrp, Ggens, M.generators );
fi;

if oper=fail then
Expand Down
23 changes: 23 additions & 0 deletions tst/testbugfix/2026-08-14-AutomorphismGroupSolvableGroup.tst
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,23 @@
# Several errors or wrong results were briefly produced by
# AutomorphismGroup respectively AutomorphismGroupSolvableGroup.
# See https://github.com/gap-system/gap/pull/6510
gap> START_TEST("2026-08-14-AutomorphismGroupSolvableGroup.tst");

#
gap> Size(AutomorphismGroup(SmallGroup(24,3)));
24
gap> Size(AutomorphismGroup(SmallGroup(147, 4)));
98784
gap> Size(AutomorphismGroup(SmallGroup(864,4675)));
10368

#
gap> Size(AutomorphismGroupSolvableGroup(SmallGroup(24,3)));
24
gap> Size(AutomorphismGroupSolvableGroup(SmallGroup(147, 4)));
98784
gap> Size(AutomorphismGroupSolvableGroup(SmallGroup(864,4675)));
10368

#
gap> STOP_TEST("2026-08-14-AutomorphismGroupSolvableGroup.tst");
Loading