[Rd] noncentral F-distributed random numbers (PR#9055)

[Thomas Lumley]

On Sat, 1 Jul 2006, longor at iastate.edu wrote:
>
> The rf() function reads:
>> rf
> function (n, df1, df2, ncp = 0)
> {
>    if (ncp == 0)
>        .Internal(rf(n, df1, df2))
>    else rchisq(n, df1, ncp = ncp)/rchisq(n, df2)
> }
> <environment: namespace:stats>
>
> where I believe both the numerator and the denominator should be divided by
> their corresponding degrees of freedom.
>

Yes. Fixed for 2.4.0.

I didn't add a denominator non-centrality parameter, since we don't have 
code for qf, pf, or df for the doubly non-central distribution.

 	-thomas