[GAP Forum] StructureDescription

A.E. Brouwer aeb at win.tue.nl
Mon Jul 7 15:08:37 BST 2008

The GAP manual advertises:
"The method for StructureDescription exhibits the structure of
 the given group to some extend using the strategy outlined below.
 The idea is to return a possibly short string which gives some insight
 in the structure of the considered group and can be computed
 reasonably quickly."

(manual typo: s/extend/extent/)

It seems to me that the idea fails. Maybe it is meant to be used only
on baby groups, say with fewer than 100 elements, but used on
rather small groups it usually crashes after many hours.
Reactions are: recursion depth overflow (at recursion depth 5000), or
memory overflow (needs more than the 3GB allowed on the command line), or
missing info in Holt/Plesken library.
This is on a 4GB machine, and Google shows me the complaint of
R. Keith Dennis who tried groups of order 256 on a 128GB machine,
and found that GAP crashed, so I need not be surprised that GAP
fails for me on groups of order 1024.

Other functions reveal the structure of the groups involved rather quickly.
I wonder what StructureDescription tries to do that is so extremely expensive.

Maybe the present behaviour should be regarded as buggy.
It does not live up to what the manual promises.


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