#19197: LatticePoset: add breadth()
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Reporter: jmantysalo | Owner:
Type: enhancement | Status: needs_review
Priority: major | Milestone: sage-6.9
Component: combinatorics | Resolution:
Keywords: | Merged in:
Authors: Jori Mäntysalo | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
u/jmantysalo/latticeposet__add_breadth__|
33610ad2c4327679b8dfc1d3af445fe4d9080e4a
Dependencies: | Stopgaps:
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Comment (by jmantysalo):
Replying to [comment:15 ncohen]:
> - I was very surprised to see a 'distance' argument in the depth-first-
search
> function. You do not compute the 'distance' when running a
> depth-first-search. At least not the usual notion of distance in graph
> theory. We should probably remove it, as it is *highly* dangerous to
advertise
> it this way `O_o`
For me the parameter name `distance` feels very clear. But could like also
`max_depth`. I think that it is useful to have a function that tells for
example to what cities you can reach using max three bus.
> - In your code, please use breadth-first-search instead.
Why? Doesn't it use more memory?
> - Definition of 'elems': this line often test for containment in
'too_close'. Do
> not run containment tests in a list. use a 'set' for that: containment
is
> faster.
OK.
> - Anyway, you probably should do this differently, i.e. with
> `breadth_first_search(report_distance=True)` while filtering 'too
close'
> elements according to their distance.
I can test and see what happens. But I must make some test lattices, maybe
some ordinal sum of ordinal products.
> - I still believe that it would be faster to use
> 'subsets_with_hereditary_property' inside of your code.
I am not sure about that. If I am right, it will make all 2-element
antichains, then all 3-element antichains and so on. There will be many of
them, only one is needed. (But the one must be the right one, of
course...)
> - Why do you deal with breadth 2 differently from the rest?
There was some complication with breadth 2. Maybe it is not needed now in
the near-to-final version.
And then, this depends on what one is doing. I guess it makes no
difference for a big lattice, but for `10^4` small it might be different
thing.
> Besides that, congratulations for this algorithm. It works, and it works
well.
Thanks! And thanks for the comments.
--
Ticket URL: <http://trac.sagemath.org/ticket/19197#comment:16>
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