> < ^ Date: Thu, 22 Jul 1999 08:42:28 +0200 (CEST)
> < ^ From: Thomas Breuer <Thomas.Breuer@Math.RWTH-Aachen.DE >
< ^ Subject: Re: [2] Unit groups in Sisyphos

Dear GAP Forum,

in the first half of June,
Alexander B. Konovalov replied to a forum message,
and he raised another question that has not been answered yet.
(Sorry for the delay.)

The problem was the following.

The next question is very similar to the previous one :-)
does anybody know what hardware resources are necessary to compute
normalized units group of group algebra of group of order ***256*** over
GF(2), using the function NormalizedUnitsGroupRing ?
Here I have the following situation:

gap> G:=TwoGroup(256,10);
Group( a1, a2, a3, a4, a5, a6, a7, a8 )
gap> RequirePackage("sisyphos");
gap> U:=NormalizedUnitsGroupRing(G);
#D use multiplication table
fatal error: memory exhausted
Error, output file was not readable in
NormalizedUnitsGroupRing( G ) called from
main loop

The reason for such calculation is connected with
the problem of involving of certain wreath products
into the unit group of modular group algebras

The ``fatal error'' is signalled by the standalone program
``sisyphos'' that is called by GAP.
Unfortunately the only way to increase the memory needed by
``sisyphos'' for the computation of normalizer units
is to modify the GAP code of the function
This code is in the file `pkg/sisyphos/gap/sisgprin.g' of the
GAP distribution.
For the example above, it is suficient to replace the line

SISYPHOS.SISPMEM := "300000";                            


SISYPHOS.SISPMEM := "3000000";

(Probably a smaller value would also suffice.)
With this parameter, the example needs about five minutes of
CPU time to compute the required unit group of order 2^255.

I hope this helps.

Kind regards,

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