#14019: equality is broken for Posets
-------------------------------------+-------------------------------------
Reporter: ncohen | Owner: sage-combinat
Type: defect | Status: needs_work
Priority: major | Milestone: sage-6.4
Component: combinatorics | Resolution:
Keywords: posets | Merged in:
Authors: Travis Scrimshaw, | Reviewers: Travis Scrimshaw,
Anne Schilling | Anne Schilling
Report Upstream: N/A | Work issues:
Branch: | Commit:
public/combinat/poset/fix_equality-14019|
8dddb16ee9bce94fab03989228cf83dd567f8ac0
Dependencies: #17059 | Stopgaps: #14185
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Comment (by aschilling):
Hi Nathann,
> My mistake, I was convinced that I had displayed the poset with a
`.show()` and looked at a path labelled with 0,1,2,3,... while the linear
extension was 0,9,... There is nothing wrong with this example indeed.
Ok. Why does the documentation say *unique* though? It does not make sense
to me.
> This being said, i still do not understand the code. Is the following
behaviour correct ?
>
> {{{
> sage: P =
Poset(digraphs.Path(4),['a','b','c','d'],linear_extension=True)
> sage: list(P.canonical_label())
> [0, 1, 2, 3]
> }}}
I think so. The documentation says that `canonical_label` is supposed to
label the poset with elements `\{0,1,\ldots,n-1\}`. I changed the code
slightly, so that [0,1,2,...]
is a linear extension of the canonical relabeled poset.
> I do not understand what you do with the `elements` list in
`canonical_label` given that the output is labelled with `0,1,2,3`.
Especially when `linear_extension=False` `O_o`
The documentation says that canonical relabeled means indexed by
`0,1,\ldots,n-1`. I did not write this code, so am not sure what this is
used for.
Internally, now the poset code still stores `P._hasse_diagram` as a Hasse
diagram on `0,1,\ldots,n-1` to make it light-weight and only compare
integers internally. The elements are taken from the Hasse diagram, when
`elements` is not specified. So passing a Hasse diagram that is on
`0,1,\ldots,n-1` will automatically make the element set equal to this.
Anne
PS: I fixed the doc failures that John reported except the ones in
`src/sage/modular/modform_hecketriangle`
----
New commits:
||[http://git.sagemath.org/sage.git/commit/?id=8dddb16ee9bce94fab03989228cf83dd567f8ac0
8dddb16]||{{{changes to canonical_label}}}||
--
Ticket URL: <http://trac.sagemath.org/ticket/14019#comment:63>
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