#5664: [with patch, needs review] Bugs in PermutationGroup_subgroup.__cmp__
--------------------------+-------------------------------------------------
Reporter: SimonKing | Owner: SimonKing
Type: defect | Status: new
Priority: critical | Milestone: sage-3.4.1
Component: group_theory | Keywords: comparison subgroup
--------------------------+-------------------------------------------------
Comment(by SimonKing):
Replying to [comment:9 wdj]:
> > Does this way of comparison makes kind of sense?
>
> Not in my opinion. If H, K are permutation groups, then
> H == K should return True iff H=k (as sets)
> H<K should return True iff H is a subset of K.
>
> Does your patch do this?
Apparently not.
My way of thinking was like this: The present implementation took into
account that we do not talk about permutation groups but about
''subgroups'' of permutation groups. With this in mind, it is natural to
have K==H if and only if K is the same permutation group as H, and ''in
addition'' the ambient groups coincide.
One question on gap: Assume that K is a ''proper'' subgroup of H; would
{{{K._gap_()<H._gap_()}}} return True?
If the answer to the preceding question is 'Yes' then my patch provides
the following:
* If K is a ''proper'' subgroup of H, then K<H.
* If K and H coincide as permutation groups and the ambient group of K is
a proper subgroup of the ambient group of H, then K<H
* K==H only if K coincides with H (as permutation groups) and ''in
addition'' the ambient groups coincide.
But of course it is also a very natural thing (and probably what
algebraists would expect from K<H) to just test whether one group is
subgroup of the other. If this is what {{{K._gap_()<H._gap_()}}} does,
then it is easy to implement (tomorrow, when I'll have better internet
access; now is about the 5th attempt to submit my comment...).
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/5664#comment:10>
Sage <http://sagemath.org/>
Sage - Open Source Mathematical Software: Building the Car Instead of
Reinventing the Wheel
--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"sage-trac" group.
To post to this group, send email to [email protected]
To unsubscribe from this group, send email to
[email protected]
For more options, visit this group at
http://groups.google.com/group/sage-trac?hl=en
-~----------~----~----~----~------~----~------~--~---
