[GAP Forum] Primitive Group Library problems

[Gordon Royle]

Dear Gapsters


I work with both GAP and Magma which use a different numbering system for their respective PrimitiveGroup libraries.

Therefore I keep having to work out which “Gap-number” corresponds to which “Magma-number” for particular groups.

So I decided to make a “once and for all” calculation and create a master table with the correspondence between the two numbering systems.

During routine sanity checking at the end of this process, I was surprised to discover that the two libraries contain different numbers of groups.

In particular,

gap> NrPrimitiveGroups(1575);
6

> NumberOfPrimitiveGroups(1575);
8


Closer inspection reveals that the GAP library is missing two groups - they have orders 14742000000 and 29484000000; the first one can be identified as PSU(4,5) and it is contained in the second group.



All the best

Gordon



Professor Gordon Royle
School of Mathematics and Statistics
University of Western Australia
Gordon.Royle at uwa.edu.au<mailto:Gordon.Royle at uwa.edu.au>