[Rd] contribution offer: df() for non-centrality != 0

[Peter Ruckdeschel]

Hi R-devels,

I noticed that for the scheduled R 2.3.0,
there is still no function df() for
non-centrality != 0.

Easter is quickly approaching, so as my little
gift, I would like to offer you some code to fill
this gap:

After excluding some "unusual" cases,
it amounts to differentiating the corresponding
function pnf() --- which in turn leads to the
function dnbeta() already available in the
stats package for some time.

You may find this code in

http://www.uni-bayreuth.de/departments/math/org/mathe7/R-devel/dnf.tar.gz

This archive includes the C-File    dnf.c      
as well as some adapted versions     Fdist_new.Rd   
and     distn_new.R;
in the latter two files I indicated all modifications
w.r.t.  Fdist.Rd    and    distn.R     by
a corresponding %%-tag.

You may modify these files as you like in order to
conform your design principles

--- and hopefully we will soon have df() for ncp, too...

Best,
Peter