On Sat, Oct 16, 2010 at 5:12 PM, Christian Stump
<christian.st...@gmail.com> wrote:
>> This would be an infinite group which I think is not implemented in Sage or 
>> GAP.
>> I can't even imagine a way that GAP could help, but it can't hurt to
>> ask in the GAP support list. Maybe there is an "approximation" someone could
>> think of that might help. Please be as specific as possible when formulating
>> your question though.
>
> Sorry if my question and explanation is not exact enough! I don't want
> the group of all matrices over the cyclotomics, but only a matrix
> group with some generators: E.g., I would like the following for UCF
> being the universal cyclotomic field:
>
> M = matrix( UCF, 1, [ E(3) ] )
> G = MatrixGroup( [ M ] )
>
> or, a little more interesting:
>
> gens = [ matrix( UCF, 2, [ E(3), 0, 0, E(4) ] ), matrix( UCF, 2, [ -
> E(3), 0, 0, -1 ] ) ]
> G = MatrixGroup( gens )


Does this help?

sage: K = CyclotomicField(12)    # 12 = 4*3
sage: K.gens()
(zeta12,)
sage: z = K.gens()[0]
sage: z
zeta12
sage: E3 = z^4
sage: E4 = z^3
sage: gens = [ matrix( K, 2, [ E3, 0, 0, E4 ] ), matrix( K, 2, [ -E3,
0, 0, -1 ] ) ]
sage: G = MatrixGroup( gens )
sage: G.order()
24


>
> The same is already possible in gap:
>
> gap> G := GroupWithGenerators( [ [[E(3)]] ] );
> Group([ [ [ E(3) ] ] ])
> gap> Number( Elements( G ) );
> 3
> gap> G := GroupWithGenerators( [ [[E(3),0],[0,E(4)]], [[-E(3),0],
> [0,-1]] ] );
> Group([ [ [ E(3), 0 ], [ 0, E(4) ] ], [ [ -E(3), 0 ], [ 0, -1 ] ] ])
> gap>
> Number( Elements( G ) );
> 24
>
> I thought, having UCF in sage available, this would be nice to have as
> well.
>
> Thanks, Christian
>
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