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Dear Forum, dear Nicola Sottocornola,

[...] A and S are 4x4 matrices over Cyclotomics

G:=Group(A,S);;

D:=DerivedSubgroup(G);

K:=Group(GeneratorsOfGroup(D),S);

Size(K);

exceeded the permitted memory (`-o' command line option) at

[...]

brk>

The problem here is the wrong use of the function `Group'. Type

gap> ?Group

to read the manual section for this function.

When it is called as for your group K the second argument is interpreted as

the identity of the group (the first argument is a list of generators).

Since S is not the identity matrix, GAP created a nonsense object here and

runs into an error when you ask for `Size(K);'. We will think about putting

a check of the input into the code in future GAP releases.

What you actually wanted to tell GAP was:

G:=Group(A,S);;

D:=DerivedSubgroup(G);

# Now you just give one list of generators

K:=Group(Concatenation(GeneratorsOfGroup(D), [S]));

Size(K);

I hope this helps,

Frank

/// Dr. Frank Lübeck, Lehrstuhl D für Mathematik, Templergraben 64, /// \\\ 52062 Aachen, Germany \\\ /// E-mail: Frank.Luebeck@Math.RWTH-Aachen.De /// \\\ WWW: http://www.math.rwth-aachen.de/~Frank.Luebeck/ \\\

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