Re: Help with nchoosek

[Michael Godfrey]

> Error using nchoosek (line 48)
> K must be an integer between 0 and N.
>
> >> nchoosek ([4 5], 8)
>
> ans =
>
>    Empty matrix: 0-by-8
> -----------------------------------------------------------------
>
> I find this behaviour of Matlab rather unfortunate. Actually, I would 
> have defined the output to be 0 and [0 0].
>
> Having nchoosek (n, k) be 0 when k > n is a very useful convention 
> that make lots of combinatorial formulas easier to write (and prove).
>
> This is for instance the behaviour of R:
>
> -----------------------------------------------------------------
> > choose (5, 8)
> [1] 0
> > choose (c(4, 5), 8)
> [1] 0 0
> -----------------------------------------------------------------
>
> and Python + SciPy:
>
> -----------------------------------------------------------------
> >>> from scipy.special import binom
> >>> binom(5, 8)
> 0.0
> >>> binom((4, 5), 8)
> array([ 0.,  0.])
> -----------------------------------------------------------------
>
> @++
> Julien
This is a good case for compatibility with R.  And, it would ba appropriate
to document that the incompatibility with Matlab is intentional.

Michael