[GAP Forum] Will my program ever finish?

[Alexander Hulpke]

Dear Forum, Dear Gordon,

GAP always calls a randomized Schreier-Sims but then calls a verification routine.
I suspect GAP is in this verification routine. (You could interrupt with CTRL-C and call Where(500) to see the function callback to check.)

Basically there are three ways to get this faster:

- Skip most verification:

StabChainOptions(G).random:=1;

- Assign an order as known:

SetOrder(G,9170703360);

- Use the genss package (which performs better for huge degree groups but currently has no verification step).

Best,

   Alexander



> On Jun 24, 2015, at 6:37 PM, Gordon Royle <gordon.royle at uwa.edu.au> wrote:
> 
> I have four permutations, each of which has degree 76422528 (for those interested, this is the degree of a primitive representation of PSp(6,3)).
> 
> The permutations generate a group, which I believe to have order 9170703360 (this is twice the order of PSp(6,3)).
> 
> For various reasons, I wish to know how the extra factor of 2 is acting.
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> I can read the four permutations into GAP, and I can form the group generated by them, but now I need to compute with it.
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> I have just asked GAP for the order of the group, both for double-checking, and also so that it sets up the internal data structures needed for further computation.
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> 
> But now it is sitting there, consuming cpu-time, but with no other indication of progress.
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> Initially it chewed up memory quite quickly for a while, but it has stabilised and seems to just be grinding on in the same memory footprint - I left it overnight, and the memory used has been constant.
> 
> 
> Is there any way that I can guess whether this will finish (a) tonight, (b) tomorrow, or (c) just before the sun goes supernova?
> 
> Alternatively, can I “help” it by *telling* GAP the order of the group? (In Magma, I can _assign_ the order of the group and then use RandomSchreier to generate a bases/s.g.s). Of course, I lose the double-checking aspect of things, but I’m willing to do that if necessary.
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> Thanks
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> Gordon
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