Dear Forum, Dear Benjamin Sambale,
G:=AlternatingGroup(4);
N:=Subgroup(G,[(1,2)(3,4),(1,3)(2,4)]);
H:=DirectProduct(CyclicGroup(2),CyclicGroup(2));
A:=AutomorphismGroup(H);
P:=SylowSubgroup(A,3);
epi:=NaturalHomomorphismByNormalSubgroup(G,N);
iso:=IsomorphismGroups(FactorGroup(G,N),P);
f:=CompositionMapping(IsomorphismGroups(FactorGroup(G,N),P),epi);
SemidirectProduct(G,f,H);
After the command "SemidirectProduct(G,f,H);" GAP returns:
"Error, not ready yet, only finite polycyclic groups are allowed"
But every group in my example is finite polycyclic, even the
semidirect product would be. I can't imagine, what should be the
problem in constructing semidirect products.
The problem is that G is not a PC group and the method for PC groups
claims to apply (because G is solvable), but the presentation GAP
finds for G (likely looked up, as the group is alternating) is not a
pc presentation.
This will be fixed in the next bugfix (the method should not apply,
there is a fallback method that does conversion of the
representation), in the meantime a workaround would be to convert both
groups (G and H) into permutation groups (or -- if solvable -- pc
groups).
Best wishes,
Alexander Hulpke
-- Colorado State University, Department of Mathematics,
Weber Building, 1874 Campus Delivery, Fort Collins, CO 80523-1874, USA
email: [email protected], Phone: ++1-970-4914288
http://www.math.colostate.edu/~hulpke
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