Opened 11 years ago
Closed 9 years ago
#9890 closed defect (fixed)
A proper random_element() method for PerfectMatchings
Reported by: | ncohen | Owned by: | sage-combinat |
---|---|---|---|
Priority: | major | Milestone: | sage-5.10 |
Component: | combinatorics | Keywords: | |
Cc: | nthiery, fhivert | Merged in: | sage-5.10.beta5 |
Authors: | Nathann Cohen | Reviewers: | Frédéric Chapoton |
Report Upstream: | N/A | Work issues: | |
Branch: | Commit: | ||
Dependencies: | Stopgaps: |
Description
At the moment, the method random_element()
from PerfectMatchings? computes a random matching by picking a random integer between 0 and the number of matchings on n elements, then (I presume) enumerating all the matchings according to some ordering until the k
th has been computed. This is impressively useless.
sage: %timeit PerfectMatchings(12).random_element() 5 loops, best of 3: 1.5 s per loop
By the way, I was not able to write a method to obtain the list of pairs describing the matching from an PerfectMatching? object.. I don't understand how this class is written, and I have no idea why it needs to be so complicated (but it would be nice to add it to this ticket during the review, if someone gets how it works).
The method random_element (and also an_element) both raise an exception when the set of elements is EMPTY. I also fixed the doctests.
(I don't even get why you can build a PerfectMatchings? class on an odd number of elements in the first place)
I expect this ticket could be heavily modified during review, but there is a problem with these classes at the moment.
Nathann
Attachments (2)
Change History (8)
comment:1 Changed 9 years ago by
- Cc nthiery fhivert added
comment:2 Changed 9 years ago by
- Status changed from new to needs_review
Patch updated ! On the way, I also fixed this "small problem" :
sage: PerfectMatchings(3).an_element() [(1, 2)]
Nathann
Changed 9 years ago by
comment:3 follow-up: ↓ 4 Changed 9 years ago by
hello,
looks good to me.
I have taken the opportunity to make a complete cosmetic clean-up of the file (using pep8 and pyflakes)
if my review patch is ok for you, you can set a positive review
Changed 9 years ago by
comment:4 in reply to: ↑ 3 Changed 9 years ago by
- Reviewers set to Frédéric Chapoton
- Status changed from needs_review to positive_review
I have taken the opportunity to make a complete cosmetic clean-up of the file (using pep8 and pyflakes)
if my review patch is ok for you, you can set a positive review
Okayyyyyyy ! Good to go, then :-)
By the way, how do you use pep8 and pyflakes ? Do you run them externally on files or do you have a way to use them ?
Nathann
comment:5 Changed 9 years ago by
Yes, I just run them on the *.py files. Pyflakes is more important, as it finds missing imports and unused variables. Pep8 is much more for the cosmetic, but can check that raise statements are in python3 syntax and find other deprecated syntax.
comment:6 Changed 9 years ago by
- Merged in set to sage-5.10.beta5
- Resolution set to fixed
- Status changed from positive_review to closed
I forgot to click on
needs_review
three years agoT_T
Nathann