[GAP Forum] Finding certain subgroups from very large group

[Stephen Linton]

Dear Kher Sham Lim,

I assume you actually want to know if G has a subgroup isomorphic to H.
If so, the command you want is IsomorphicSubgroups(G,H).

This is enormously more efficient than simply listing all [conjugacy classes of] subgroups of G in most cases.

It might also be helpful to first replace G by an isomorphic permutation group (using IsomorphismPermGroup).

All of these commands are documented in the reference manual (equivalently in the on-line help).

	Steve

On 1 Feb 2013, at 11:33, Kher Sham Lim <khersham.lim at mpi-hd.mpg.de> wrote:

> Dear GAP forum
> 
> I have a very large group to study, say G (it is an automorphism group 
> of a small group). G has order of 10 million and I am interested in 
> knowing whether a certain known group, say H is a subgroup in G. To find 
> H is impossible in GAP, as GAP tries to calculate all the subgroups and 
> this process exceeds my computer's memory. Is there another command or 
> algorithm in GAP to compute subgroup of specific order only, or at least 
> limit the subgroup order? I used SONATA to obtain the subgroups by the 
> way. Thanks in advanced.
> 
> Sincerely
> 
> Kher Sham Lim
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