#19686: Category of posets: lower_set() broken
---------------------------------+-------------------------
Reporter: jmantysalo | Owner:
Type: defect | Status: new
Priority: minor | Milestone: sage-6.10
Component: combinatorics | Resolution:
Keywords: poset | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
---------------------------------+-------------------------
Old description:
> {{{
> P = Posets.PentagonPoset()
> print P.principal_order_ideal(3)
> print P.principal_lower_set(3)
> print P.order_ideal([3])
> print P.lower_set([3])
> }}}
>
> gives
>
> {{{
> [0, 2, 3]
> [0, 2, 3]
> [0, 2, 3]
> TypeError: 'NotImplementedType' object is not callable
> }}}
>
> And this seems like a bug. CC to nthiery as this probably relates to
> category code.
New description:
{{{
P = Posets.PentagonPoset()
print P.principal_order_ideal(3)
print P.principal_lower_set(3)
print P.order_ideal([3])
print P.lower_set([3])
}}}
gives
{{{
[0, 2, 3]
[0, 2, 3]
[0, 2, 3]
TypeError: 'NotImplementedType' object is not callable
}}}
And this seems like a bug. Same applies to `upper_set`.
--
Comment (by jmantysalo):
Replying to [comment:1 nthiery]:
> By the way: the rationale for those aliases is that, in the long run, I
am in favor of migrating from `order_ideal` to `lower_set`: the former is
ambiguous with two distinct widely accepted meanings in the community.
I never remember which one is "ideal" and which "filter". Hence "lower
(/upper) set" is better. OTOH the order ideals lattice of a poset is
established term.
> Note: this is about (the abstract classes for) posets ; not to the
category infrastructure.
Yep. But you may know what to do with `@abstract_method` that seems to be
the difference between `lower_set` and `principal_lower_set`. I do not.
--
Ticket URL: <http://trac.sagemath.org/ticket/19686#comment:2>
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