id summary reporter owner description type status priority milestone component resolution keywords cc merged author reviewer upstream work_issues branch commit dependencies stopgaps
9890 A proper random_element() method for PerfectMatchings ncohen sage-combinat "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" defect closed major sage-5.10 combinatorics fixed nthiery fhivert sage-5.10.beta5 Nathann Cohen Frédéric Chapoton N/A