[GAP Forum] Small groups library, recent changes

[Hulpke,Alexander]

Dear GAP-Forum,

The new release, GAP 4.11, contains a new version, 1.4.1 of the small groups library (the smallgrp package).

The only change in this relase concerns the numbering of the groups in orders p^7 for p=3,5,7,11.  None of this concerns completeness or correctness of the underlying classification, but the change is relevant if you ever referred to a group of one of these orders (and only these orders) by its index number, that is as `SmallGroup(order,indexnr)`.

The classification of p-groups, that is the p-group generation algorithm for a particular order iterates through classes (given by nilpotency class, isomorphism classes of factor groups, etc.) of groups and then generates the groups in each class. The numbering is obtained by simply concatenating these groups from the different classes.
After the release of version 1.0 of the smallgrps package we noted that the arrangement of classes for the concatenation (and thus the numbering of groups) had been chosen differently between GAP and Magma. An attempt to fix this had been made in version 1.1 of smallgrp, but this attempt used a wrong permutation. We have corrected this mistaken, thus changing the ordering for orders p^7, p=3,5,7,11, once more. We are grateful to Mark Lewis for pointing out this issue.

With the change to version 1.4.1, the numbering of groups of order p^7, p=3,5,7,11, agrees with the ordering in Magma, Version 2.23. This has been checked by explicit comparisons of pc presentations. It is our firm intention to keep this ordering stable, thereby allowing for consistent reference to groups. (We cannot make any promises for what Magma will do, but do not have any reason to believe that its ordering will change either.)

If you need to refer to groups by the older numbering, please see the manual section on SMALL_GROUPS_OLD_ORDER.

Again, the numbering of the library for all other orders has been unaffected and, as promised, will remain stable.

Regards,

   Alexander Hulpke

-- Colorado State University, Department of Mathematics,
Weber Building, 1874 Campus Delivery, Fort Collins, CO 80523-1874, USA
email: hulpke at colostate.edu<mailto:hulpke at colostate.edu>,  http://www.math.colostate.edu/~hulpke