[GAP Forum] StructureDescription

A.E. Brouwer aeb at win.tue.nl
Tue Jul 8 08:49:43 BST 2008

Hi Keith,

> 2.  A slightly modified version of the program works substantially
>     faster and with less memory; it's my understanding it will be in
>     the next version of gap.  (Thanks Burkhard!)

Where is it?

> 3.  Crashing: ...

(I described not the "Segmentation fault" type of crash, but the
"recursion depth exceeded" / "memory exceeded" / "Holt/Plesken incomplete"
types of failure.)

> 4.  Which group(s) of order 1024?  I'd be intersted in seeing if the
>     new version of StructureDescription can handle them.

Easier if you provide that new version. This happens in real life,
not a group from some library.


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

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