Re: numtoperm and Factorial Number System

[Joerg Arndt <arndt@jjj.de>]

Please ask Max Alekseyev!
IIRC he such code, even for multiset-permutations.

While we are at combinatorial generation,
are there plans for other types of objects
(e.g. partitions, and set partitions)?

Best regards,  jj


* Karim Belabas <Karim.Belabas@math.u-bordeaux1.fr> [Oct 07. 2012 18:03]:
> * Mathieu Carbou [2012-10-07 01:56]:
> [...]
> > I was wondering why in PARI the numtoperm does not match the Nth
> > permutation in the factorial number system ?
> 
> No particular reason. The code was submitted (by Ilya Zakharevich) and
> included essentially "as is".
> 
> > Is there a way to use numtoperm to get the good result or I have to code
> > a function which decompose the number in the factorial number system by
> > myself ?
> 
> Not currently. There's a long-standing wishlist item in the Bug Tracking System
> 
>   http://pari.math.u-bordeaux1.fr/cgi-bin/bugreport.cgi?bug=899
> 
> asking for a lexicographic ordering (aka Lehmer code). If someone has a
> GP or C implementation for this, I have no objection to replacing the
> current code.
> 
> [ The current numtoperm / permtonum code should be modified anyway to
> return / accomodate t_VECSMALLs: it's more efficient and permutations are
> now represented by t_VECSMALLs anyway. This way they can be inverted,
> multiplied, etc. ]
> 
> Cheers,
> 
>     K.B.
> -- 
> Karim Belabas, IMB (UMR 5251)  Tel: (+33) (0)5 40 00 26 17
> Universite Bordeaux 1          Fax: (+33) (0)5 40 00 69 50
> 351, cours de la Liberation    http://www.math.u-bordeaux1.fr/~belabas/
> F-33405 Talence (France)       http://pari.math.u-bordeaux1.fr/  [PARI/GP]
> `