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gap-packages / sgpdec

GAP package for Hierarchical Composition and Decomposition of Permutation Groups and Transformation Semigroups
https://gap-packages.github.io/sgpdec/
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Wreath product regression #19

Closed egri-nagy closed 3 years ago

egri-nagy commented 3 years ago

With GAP 4.11 the wreath product construction is not working any more. It works fine with GAP 4.10.2.

# Input is:
ForAll(triples, function(t)
 local A,B,C,AB,BC,ABC,AB_C,A_BC;
 A := t[1];
 B := t[2];
 C := t[3];
 AB := Image(IsomorphismPermGroup(GroupWreathProduct([A,B])));
 BC := Image(IsomorphismPermGroup(GroupWreathProduct([B,C])));
 ABC := Image(IsomorphismPermGroup(GroupWreathProduct([A,B,C])));
 AB_C := Image(IsomorphismPermGroup(GroupWreathProduct([AB,C])));
 A_BC := Image(IsomorphismPermGroup(GroupWreathProduct([A,BC])));
 return IsomorphismGroups(ABC,A_BC)<>fail
        and
        IsomorphismGroups(ABC,AB_C)<>fail; end);
# Expected output:
true
# But found:
false
########
fingolfin commented 3 years ago

To track this down might be helpful to do a git bisect on the GAP repository. If anyone wants to try, the script etc/bisect.sh included with GAP helps with that.

egri-nagy commented 3 years ago

In GAP 4.10.2:

gap> Z2:=CyclicGroup(IsPermGroup,2);
Group([ (1,2) ])
gap> Image(IsomorphismPermGroup(GroupWreathProduct([Z2,Z2])));
Group([ (1,3)(2,4), (1,2) ])

while in GAP 4.11 we get

ap> Z2:=CyclicGroup(IsPermGroup,2);
Group([ (1,2) ])
gap> Image(IsomorphismPermGroup(GroupWreathProduct([Z2,Z2])));
Group([ (1,5)(2,6)(3,7)(4,8), (1,3)(2,4)(5,6)(7,8) ])

which causes trouble since we use them as permutation groups. I'll try whether asking for a smaller representation fixes the test.

egri-nagy commented 3 years ago

fixed by 06eecb697f69ced7ab7c45b7df5ccf3f6c04780c

nehaniv commented 3 years ago

hi @, Maybe there's a bug elsewhere - I just saw the discussion is [semigroups/Semigroups] from Tom Conti-Leslie and Wilf Wilson , but maybe it's not relevant, that it is sometimes giving wrong 'isomorphisms' though it seems to be a problem already with GAP 10.4.2. Best, X

On Mon, Jan 4, 2021 at 5:28 AM Attila Egri-Nagy @.***> wrote:

With GAP 4.11 the wreath product construction is not working any more. It works fine with GAP 4.10.2.

Input is:

ForAll(triples, function(t) local A,B,C,AB,BC,ABC,AB_C,A_BC; A := t[1]; B := t[2]; C := t[3]; AB := Image(IsomorphismPermGroup(GroupWreathProduct([A,B]))); BC := Image(IsomorphismPermGroup(GroupWreathProduct([B,C]))); ABC := Image(IsomorphismPermGroup(GroupWreathProduct([A,B,C]))); AB_C := Image(IsomorphismPermGroup(GroupWreathProduct([AB,C]))); A_BC := Image(IsomorphismPermGroup(GroupWreathProduct([A,BC]))); return IsomorphismGroups(ABC,A_BC)<>fail and IsomorphismGroups(ABC,AB_C)<>fail; end);

Expected output:

true

But found:

false ########

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