[GAP Forum] Stop GAP from storing group properties

[Dima Pasechnik]

On Sat, May 08, 2021 at 10:07:00AM +0000, Stefan Kohl wrote:
> Dear Marc,
> 
> there are at least two ways to achieve this.
> -- One of them is to use the function `AttributeValueNotSet',
> and another is to only pass the generators of the group to your testing function,
> and to create the group object locally inside that function.

I just wanted to mention Unbind(), a GAP function which allows one to remove
components from records, etc. - check its docs.

And (no longer documented?) GASMAN("collect")
to explicitly trigger garbade collection, something that might help keeping
memory consumption at bay.

HTH
Dima
 

> 
> Does this help you? --
> Let me know if you have any further questions!
> 
> Best regards,
> 
>     Stefan
> 
> 
> ________________________________
> From: Marc Keilberg <keilberg at usc.edu>
> Sent: Saturday, May 8, 2021 4:01 AM
> To: GAP Forum <Forum at gap-system.org>
> Subject: [GAP Forum] Stop GAP from storing group properties
> 
> Dear  GAP Forum,
> 
> I've been looking to sift through a particular family of a few ten-thousand
> groups, which are not in any of the current libraries, to see if they have
> certain properties.  While it's relatively easy to construct the entire
> family of groups via the anupq package, and the test I run on them is
> relatively quick (a second or two per group on my computer), I run into
> serious memory consumption issues when I go to start testing them all (with
> a function specifically written to perform the test in question).  While
> the list of groups I want only takes up a few gigabytes, and each iteration
> of the testing function should be consuming a small fraction of that before
> it completes, my total memory consumption constantly ticks up as I run
> through the list, ultimately consuming well more memory than the list of
> groups itself.
> 
> The problem, best as I can tell, is that in my function I must compute
> RationalClasses(Center(G)) for the given group G, and this information is
> getting stored in the group, resulting in ever increasing amounts of memory
> consumption as GAP iterates over my list of groups.  But I don't want or
> need it stored.  I have tried using ShallowCopy, but that doesn't help, as
> the group objects are all non-copyable apparently, so ShallowCopy,
> Immutable, StructuralCopy etc. all just return the original object instead
> of a wholly new one.  So it's still storing the information on the original
> group object, instead of a distinct copy that gets deleted upon the
> function completing.
> 
> So is there any way I can prevent a testing function from storing
> properties of a group on that group after it completes, or otherwise delete
> any newly stored information before the function exits, and thereby prevent
> this excess memory consumption?
> 
> Thanks,
> Marc
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