#21122: Do not force non-facade posets as the indexing set for the Möbuis
algebra
basis
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Reporter: tscrim | Owner:
Type: defect | Status: needs_review
Priority: major | Milestone: sage-7.3
Component: combinatorics | Resolution:
Keywords: poset | Merged in:
Authors: Travis Scrimshaw | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
public/combinat/moebius_algebra_basis_keys-21122|
c09d3b086d3ba180743d7bc02ba150783ca76d4d
Dependencies: #21054, #21043 | Stopgaps:
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Comment (by darij):
Great job! Two things, though:
- I suggest replacing the doc of `_Key` by something more readable:
{{{
Helper class to serve as a key for comparing elements of the
lattice.
The change-of-basis morphisms between the bases of the
:class:`MoebiusAlgebra` are triangular with respect to the partial
order of the poset. Since this partial order might not agree with
the standard comparison function ``cmp``, we need a wrapper around
the elements of the lattice which ensures that calling ``cmp`` on
them (when wrapped) actually compares them using the lattice's
partial order. This helper class is precisely that.
}}}
(You probably can do better.)
- Do we know that whatever the `module_morphism` infrastructure does to
`key` allows `key` to live in a poset? I see `leading_item` being called
in
https://github.com/sagemath/sage/blob/develop/src/sage/modules/with_basis/morphism.py
; what does this return when there are several maximal items?
--
Ticket URL: <https://trac.sagemath.org/ticket/21122#comment:2>
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