[GAP Forum] Error in NormalSubgroups

[dmitrii.pasechnik at cs.ox.ac.uk]

On Thu, Feb 15, 2018 at 02:16:47AM -0500, David Roe wrote:
> In my version of GAP (4.8.6 included in Sage, with the SmallGroups library
> added), the following command produces an error:
> 
> gap> NormalSubgroups(SmallGroup(1458,1180));
> Error, List Element: <list>[4] must have an assigned value in
>   if map[d] > max  then
>     elm := id;
> else
>     if not IsBound( map[d] )  then
>         Error( "<elm> lies not in group defined by <pcgs>" );
>     fi;
>     ll := LeadingExponentOfPcElement( pa, elm );
>     lr := lc[d];
>     exp[map[d]] := ll / lr mod ros[d];
>     elm := LeftQuotientPowerPcgsElement( pcgs, map[d], exp[map[d]], elm );
> fi; at /home/roed/sage/local/gap/latest/lib/pcgsind.gi:1411 called from
> ExponentsOfPcElement( NumeratorOfModuloPcgs( pcgs ), elm, pcgs!.depthMap )
> at /home/roed/sage/local/gap/latest/lib/pcgsmodu.gi:931 called from
> ExponentsOfPcElement( ocr.modulePcgs, x ) at
> /home/roed/sage/local/gap/latest/lib/onecohom.gi:264 called from
> ocr.moduleMap( n ) at /home/roed/sage/local/gap/latest/lib/onecohom.gi:339
> called from
> ocr.listToCocycle( lc ) at /home/roed/sage/local/gap/latest/lib/
> grplatt.gi:1926 called from
> opr( Zero( vs ), k ) at /home/roed/sage/local/gap/latest/lib/grplatt.gi:1932
> called from
> ...  at line 1 of *stdin*

This is due to Sage not supplying GAP package crisp, which is needed for
this computation to work (on the stock installation of GAP 4.8.6, too).
Crisp can be installed into Sage's installation of GAP, fixing this, so this is a
minor issue.

The need for crisp to complete this computation is gone in GAP 4.9, as
far as I can tell, although after loading crisp GAP switches to using
it, as can be seen by difference in output formatting.

Hope this helps,
Dima

> 
> I tried installing the most recent version of GAP from source to see if the
> error was also present there, but ran into a build error:
> 
> checking for GAP architecture... x86_64-apple-darwin16.7.0-gcc-default64
> 
> ********************************************************************
>   ERROR
> 
>   Found a GAP installation at /Users/roed/sage/gap4r8 but could not find
>   information about GAP's architecture in the
>   file /Users/roed/sage/gap4r8/sysinfo.gap or did not find the directory
>   /Users/roed/sage/gap4r8/bin/x86_64-apple-darwin16.7.0-gcc-default64.
>   This file and directory should be present: please check your
>   GAP installation.
> ********************************************************************
> 
> configure: error: Unable to find plausible GAParch information.
> = Failed to build xgap-4.26
> 
> 
> Does anyone else see this error in finding the normal subgroups of
> SmallGroup(1458, 1180)?  I'm able to successfully execute this command for
> many other groups in the table of small groups....
> 
> Thanks,
> David
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