[GAP Forum] Serialisation

[Alexander Konovalov]

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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