[GAP Forum] Error computing a stabilizer in GAP 4.10.2

[Christopher Jefferson]

I suspect what's happening is often GAP's algorithms happen to output things in a sorted order, and GAP will automatically treat a sorted List as a Set, so I can (for example) treat the list [2,4,6] as a set (in fact, there is no real difference in GAP between a Set, and a List which is sorted).

Chris

________________________________________
From: Josh Hunt <joshuahunt at math.ku.dk>
Sent: 25 November 2019 08:42
To: Marc Keilberg
Cc: forum at gap-system.org
Subject: Re: [GAP Forum] Error computing a stabilizer in GAP 4.10.2

Sorry, I should have explained more: in GAP, a set is implemented as a sorted list without any "holes" or duplicate entries <https://www.gap-system.org/Manuals/doc/ref/chap21.html#X80CDAF45782E8DCB>.

I would assume that for all the other conjugacy classes, it happens to be the case that calling List(AsList(T), AsList) returns sorted lists, while for this last case the default ordering isn't sorted. I don't know how GAP sorts lists of group elements, however, so can't explain it more deeply than that!

Josh
________________________________
From: Marc Keilberg [keilberg at usc.edu]
Sent: 25 November 2019 09:32
To: Josh Hunt
Cc: forum at gap-system.org
Subject: Re: [GAP Forum] Error computing a stabilizer in GAP 4.10.2

It seems using Set(AsList(T),AsList), or any variation that uses Set instead of List as the outer call, also works.  I'm still curious about why it seemed to have no issues with any other conjugacy classes, and why this one was different, but at least this appears to be a way to avoid the issue popping up.

Thanks,
Marc
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