Well that's embarrassing. I should have read the definition more carefully.
> Date: Wed, 26 Feb 2014 08:31:45 -0700 > From: [email protected] > To: [email protected] > Subject: Re: [Jprogramming] Combinatorial Maths with J > > ((!3)*!(7-3))%~!7 > > 35 > > 3!7 > > 35 > > > On Wed, Feb 26, 2014 at 8:25 AM, Jon Hough <[email protected]> wrote: > > > I have a question about doing combinations and permutations with J. > > There is an easy to use factorial function (or is that verb) : ! > > !5120 > > Is there a combination verb? Or do I make my own? > > ((!3)*!(7-3))%~!7 > > Gives 7 choose 3. I think I butchered that. Is there a better way to do > > this, without all the brackets? > > Now I want to think about more complicated combinatorial objects: Steiner > > Systemshttp://en.wikipedia.org/wiki/Steiner_system > > Essentially a Steiner System is defined by three numbers a,b,c such that > > we have a total of c points and we collect the points into subsets of size > > b, such that for any "a" points (where a < b < c) there is exactly one > > subset containing all three:example a,b,c=2,3,7 we have the S(2,3,7) > > steiner system with points 0~6, the subsets are012 034 056 135 146 > > 236 245Note, every pair of points is in exactly one subset. > > For a given Steiner system, to calculate the number of subsets (in the > > above case 7) there is a simple eqn: > > num = (c choose a)/(b choose a) > > I would like to write this as a verb (preferrably tacit).I have > > immediately run into a problem:this verb would take three arguments. Not > > sure how to do that. > > I would like some help writing this verb. Thanks in advance. > > Regards,Jon > > ---------------------------------------------------------------------- > > For information about J forums see http://www.jsoftware.com/forums.htm > > > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
