[GAP Forum] Serialisation

[Sandeep Murthy]

Thanks.

Sandeep Murthy
s.murthy at mykolab.com

> On 12 Feb 2015, at 23:42, Alexander Konovalov <alexk at mcs.st-andrews.ac.uk> wrote:
> 
> Hi Sandeep,
> 
> As it was already noted here, the cause of the problem is that one of
> these two groups is a permutation group and the other - pc group. The
> GAP manual has a section "Saving a Pc Group" which may help you:
> 
> http://www.gap-system.org/Manuals/doc/ref/chap46.html#X85696AB9791DF047
> 
> - see GapInputPcGroup there.
> 
> Also, for pc groups you may use the pair of functions CodePcGroup and
> PcGroupCode, see them here:
> 
> http://www.gap-system.org/Manuals/doc/ref/chap46.html#X8041C2D88721EEA9
> 
> These were invented to store large libraries of small groups, and for
> really huge groups, they will may work slow. However, GapInputPcGroup
> performs quite well - I've found the log file for a group of order 3^728
> which I was saving several years ago. The group was saved in 9 seconds
> and restored in 12 seconds, and the file size was "only" 6.5 MB (gzipped
> - 1.5 MB):
> 
> gap> PrintTo( "save", GapInputPcGroup( V, "V729_13" ) );
> gap> time;
> 9217
> gap> Read("save");
> #I A group of order
> 2209395351413957253683909547381599161963288912918954731542644224734870827044293093746906\
> 7135836134418530028589701635375804525993982486739360716170312948236428294558462634156750\
> 2928525358477130679078983517688062896651637532904132693253013488158239242149787728540685\
> 561563573806847600207803782218928387605966850445847423444996735145737566710612948961
> has been defined.
> #I It is called V729_13
> gap> time;
> 12154
> gap>
> 
> Hope this helps,
> Alexander
> 
> 
> 
> On 11 Feb 2015, at 14:05, Sandeep Murthy <s.murthy at mykolab.com> wrote:
> 
>> Hi
>> 
>> I am trying to use the IO_PickleToString() method from the SCSCP package
>> to test out how GAP serialises group objects.  This does not appear to be
>> working as expected on the isomorphic groups Sym(3) and D_6 (dihedral group).
>> 
>> gap> IO_PickleToString( SymmetricGroup( 3 ) );
>> "PRMGILIS\>2PERM\>7(1,2,3)PERM\>5(1,2)INTG\>16FAIL”
>> 
>> This looks OK but for D_6 it fails:
>> 
>> gap> IO_PickleToString( DihedralGroup( 6 ) );
>> Error, no method found! For debugging hints type ?Recovery from NoMethodFound
>> Error, no 1st choice method found for `IO_Pickle' on 2 arguments called from
>> IO_Pickle( s, obj ); called from
>> <function "IO_PickleToString">( <arguments> )
>> called from read-eval loop at line 20 of *stdin*
>> you can 'quit;' to quit to outer loop, or
>> you can 'return;' to continue
>> brk>
>> 
>> Why is this?  Both should return OpenMath strings.
>> 
>> Sandeep
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>