#14319: Automorphism group with labeled vertices
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Reporter: ncohen | Owner: jason,
Type: enhancement | ncohen, rlm
Priority: major | Status: closed
Component: graph theory | Milestone: sage-5.10
Keywords: | Resolution: fixed
Authors: Nathann Cohen | Merged in:
Report Upstream: N/A | sage-5.10.beta2
Branch: | Reviewers: Volker
Dependencies: #14291, #14250, #14477, | Braun
#14435 | Work issues:
| Commit:
| Stopgaps:
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Comment (by ncohen):
> I'm confused. What is the problem with renaming the current
`p.domain()` to `p.list()`, and saying `p.list()` is going to return the
list representation of the permutation (in terms of the domain)? That's
how it always was---but before, the domain was always [1...n]. In other
words, if you aren't using the domain argument of the permutation group,
p.list() does what it always has done. If you are using the domain
argument, it makes sense that `p.list()` will speak in terms of the
domain.
I am only worried of what I saw in the code of Permutations : that there
are assumptions made by some developpers which are not known by others,
and that code will end up being broken because the assumptions are never
checked. `.list()` does not *mean* that "the output represents the
permutations when the elements are integers". Having a `.to_permutation()`
function which would return a `Permutation` object (i.e. that only handle
integers) and a dictionary associating the elements of the
`PermutationGroupElement` to integers is okay.
I just want to be sure that the code stays correct. Right now the list
that is returned by `.list()` is a private attribute, and with a name like
that there is absolutely no reason to believe that a code which creates
this private attribute should ensure the property that you expect.
Exactly like the labeling of a poset's vertices with integers is a linear
extension : that is assumed nearly everywhere in poset code, and you will
sweat for a while before finding it out. If this variable was named
"linear_extension" there would be no problem, though.
And changing the code of `list` to ensure that the list it returns
satisfies the property that you expect would ensure that the code is good,
but `.list()` really isn't right name for such a function. If you need
"the integer permutation represented by a `PermutationGroupElement`, it
looks like what you want is a way to create a Permutation object from a
`PermutationGroupElement`.
Well. What do you think ?
Nathann
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Ticket URL: <http://trac.sagemath.org/ticket/14319#comment:60>
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