#17216: Poset / LatticePoset: [meet|join]matrix algorithm
-------------------------------------+-------------------------------------
Reporter: jmantysalo | Owner:
Type: enhancement | Status: needs_review
Priority: major | Milestone: sage-6.4
Component: combinatorics | Resolution:
Keywords: | Merged in:
Authors: Jori Mäntysalo | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
u/jmantysalo/poset___latticeposet___meet_join_matrix_algorithm|
a7d2dd08623026a269f5fd7700b9e659985e7579
Dependencies: | Stopgaps:
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Changes (by jmantysalo):
* status: new => needs_review
* milestone: sage-wishlist => sage-6.4
Old description:
> First, because `meet()` is defined on `LatticePoset`, not on `Poset`, it
> is logical to also move `meet_matrix()` there.
>
> Second, `hasse_diagram.py` contains
>
> {{{
> le = copy(self.lequal_matrix())
> for i in range(n): le[i,i] = 1
> }}}
>
> This is unneeded, because `lequal_matrix()` already contains ones at
> diagonal. We can use `_leq_matrix` directly.
>
> Third, maybe the whole algorithm could be written better.
>
> All this applies dually to `join`.
New description:
Because `join()` and `meet()` are defined on [meet|join]lattices, not on
posets, it is logical to also move `join_matrix()` and `meet_matrix()`
there.
On `hasse_diagram.py` there is for example
{{{
le = copy(self.lequal_matrix())
for i in range(n): le[i,i] = 1
}}}
This is unneeded, because `lequal_matrix()` already contains ones at
diagonal. We can use `_leq_matrix` directly. There are also few other
places to small optimization.
At the same time I suggesg moving `is_lattice()` to `posets.py` from
category code, because `is_[meet|join]_semilattice()` already is there.
--
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Ticket URL: <http://trac.sagemath.org/ticket/17216#comment:5>
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