#17408: Faster transitive_reduction (=> faster Poset creation)
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Reporter: | Owner:
ncohen | Status: needs_review
Type: | Milestone: sage-6.5
enhancement | Resolution:
Priority: major | Merged in:
Component: graph | Reviewers:
theory | Work issues:
Keywords: poset | Commit:
Authors: | ce577a909e3ac2835f975cc9515b54459174e8ca
Nathann Cohen | Stopgaps:
Report Upstream: N/A |
Branch: |
u/ncohen/17408 |
Dependencies: |
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Comment (by jmantysalo):
Replying to [comment:16 nbruin]:
> > What is the rationale behind current implementation? I mean, there
must be some example where `UniqueRepresentation` makes things faster.
> However, there's something to say for it: The two posets `A={1,2,3}` and
`B={1,2,3}` with trivial relation (ie. x<=y iff x==y) are isomorphic, but
not uniquely so. So unless we're explicitly saying by what isomorphism
`A,B` are to be identified, perhaps we should treat them as not equal.
After all, `C={a,b,c}` (with empty relation) is also isomorphic to `A` and
`B` and there no-one would be tempted to say C is equal to A and B.
Thank you for very good explanation!
Generating all posets of size 7 up to isomorphism takes 18,5 second ---
this is not a bottle neck then. But with #14110 the time drops to 2,5
seconds. And when generating just Hasse diagrams instead of posets it took
0,3 second. In the code I was asked to write this is the turning point:
now slowest part is doing something with posets, not generating them.
Maybe this is so specialized case that we should let posets to be like
they are now. A user might then optimize by directly playing with Hasse
diagrams.
This optimization does not mean that you can do things with posets of size
`2n` --- it means that that you can use posets of size `n+2`.
--
Ticket URL: <http://trac.sagemath.org/ticket/17408#comment:21>
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