[GAP Forum] Exceeded Permitted Memory

[Dmitrii Pasechnik]

On Sat, May 03, 2014 at 02:03:42PM +0800, Minghui Liu wrote:
> By the way, I found that even better supercomputers are available in my
> university:
> 
> "Dedicated cluster with up to 192 CPU cores interconnected by
> high-performance InfiniBand network can be provisioned within a business
> day."
> 
> And one needs to pay to use it. Is there any point trying?
This is a distributed cluster (known as an MPP, for Massively Parallel Processor), 
i.e. you have many CPU nodes with
relatively small RAM available to each of them.
GAP won't be able to use all this memory. 

You'd rather need what is called an SMP - i.e. shared memory
(multi)processor. Indee, 
your problem is that you are running out of memory.
And not that you need more CPU cores to go faster.

What is the value of the -o parameter you are
starting GAP with?

Best,
Dmitrii

> 
> Thanks and regards,
> 
> Minghui
> 
> 
> On 3 May 2014 13:53, Minghui Liu <matliumh at gmail.com> wrote:
> 
> > Dear Forum,
> >
> > I am using GAP to compute a group with hundreds of generators and
> > relations. The command AbelianInvariants(F/relations) works perfectly, but
> > when I  use the command MaximalAbelianQuotient(F/relations); the following
> > message is returned:
> >
> > gap> phi:=MaximalAbelianQuotient(G);
> > Error, exceeded the permitted memory (`-o' command line option) in
> >   MakeImmutable( a ); called from
> > UnderlyingElement( left ) * UnderlyingElement( right ) called from
> > gen[j] ^ s[i][j] called from
> > <function "unknown">( <arguments> )
> >  called from read-eval loop at line 80 of *stdin*
> > you can 'return;'
> > brk>
> >
> > I also tried to run GAP on a supercomputer (HP Xeon four sockets 10-Core
> > and two sockets Hexa-Core 64-bit Linux cluster, CentOS 5) but with the same
> > result (Does a supercomputer make any difference at all?). Is there any way
> > that I can slove this, or should we concluded that my group is "too large"
> > to be computed by GAP.
> >
> > Anyway my goal is to find the torsion elements in F/relations. As I can
> > read from AbelianInvariants(F/relations), there are four copies of Z/Z2. Is
> > there any other way that I can find and verify the four elements in F whose
> > image has order 2 in F/relations?
> >
> > I very much appreciate your help!
> >
> > Best regards,
> >
> > Minghui
> >
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