Re: [S] Re: Factorials in S-PLUS: over-under

Vadim A Kutsyy (kutsyy@umich.edu)
Tue, 24 Mar 1998 09:52:13 -0500


Just write it:

> bin.coef<-function(n,k) gamma(n+1)/(gamma(k+1)*gamma(n-k+1))
> bin.coef(5,2)
[1] 10
> bin.coef(50,30)
[1] 4.712921e+13

But better would be:
> bin.coef<-function(n,k) exp(lgamma(n+1)-lgamma(k+1)-lgamma(n-k+1))
> bin.coef(5,2)
[1] 10
> bin.coef(50,30)
[1] 4.712921e+13

in this case it can handle larger n

Steve Bousquin wrote:
>
> I was talking about the notation for binomial coefficients (C(n,k))where
> n is over k and they are in parentheses. That part of the question was
> supposed to ask whether a function existed that would let one enter n
> and k and get (n!/k!(n-k)!).
>
> Steve Bousquin wrote:
> >
> > I can't seem to find an operator in the manuals for calculating
> > factorials. I mean !, not experiments. Also, is there a way to work
> > with the over-under type of notation?
> >
> > Steve Bousquin
>
> --
>
> ==============================================
> Steve Bousquin
>
> Colorado State University
> Department of Rangeland Ecosystem Science/GDPE
> NR209
> Fort Collins, CO 80523
> USA
>
> sbous@lamar.colostate.edu
> ==============================================
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-- 
Vadim Kutsyy
kutsyy@umich.edu
http://www.stat.lsa.umich.edu/~kutsyy
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