#10998: Categories for posets
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Reporter: nthiery
| Owner: sage-combinat
Type: enhancement
| Status: needs_work
Priority: major
| Milestone: sage-4.7.1
Component: combinatorics
| Keywords: days30
Work_issues:
| Upstream: N/A
Reviewer: Franco Saliola, Christian Stump, Nicolas M. Thiéry, Florent
Hivert | Author: Frédéric Chapoton, Christian Stump, Nicolas M. Thiéry
Merged:
| Dependencies: #11289, #10938, #9065
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Comment(by nthiery):
Hi Andrei,
Replying to [comment:21 novoselt]:
> 2) To the point: How to fix it?
>
> I really don't want to make fans unique at this point as I am planning
some adjustments to them and related objects.
>
> Does uniqueness test rely on `==` test? Is there any way to change it?
Currently `==` for fans checks that fans have the same rays and the same
generating cones in the same order. Things relates to facets require even
stronger `is`-equivalence. On the other hand, Volker votes for `==` being
mathematical equivalence without taking order into account. Such
equivalence definitely would not be acceptable deep inside implementation
which relies on fixed order.
>
> So I guess my preferred solution for now would be to trick posets into
creating different face lattices for fans and cones even if they are `==`.
Can I somehow attach `id(fan)` to the poset without altering its
structure?..
I have (finally!) just looked at this again. I traced through the
execution of {{{f.cone_containing(0)}}}, and did not find the place where
the construction of the cone (and in particular its unique representation
or not) depended on a poset. Could you give me a pointer? Or ideally, a
minimal example where two cones are constructed involving the same poset,
and where the cones should be different (but are not with this patch)?
We are both at FPSAC with Franco; it would be great if we could finish
this patch today or tomorrow.
Thanks!
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/10998#comment:33>
Sage <http://www.sagemath.org>
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