[Rd] bug in spline()? (PR#653)

[Peter Dalgaard BSA]

imsw@holyrood.ed.ac.uk writes:

> This gives c(2.5366,1.2266,-0.0834,...,1.0390). I agree with all values
> except that at x=1. The interpolation formula in Green and Silverman's
> book on splines gives the derivative of a natural spline at the first
> knot as f'(x1)=(f2-f1)/(x2-x1) -(1/6)(x2-x1)d, where d=second derivative
> at the second knot. For the above example, d=0.7071, f'(x1)=-1.3493,
> and the natural spline interpolant has value 1.2266-(-1.3493)=2.5759
> at x=1, not 2.5366.

Also, 

plot(diff(fn(seq(1,3,.01))))

reveals that something is wrong

At the other end, 

 plot(diff(fn(seq(8,11,.01))))

looks even weirder, especially if one modifies 
to y <- c(1.2266,-1.7606,-0.5051,1.01)


> PS There are different e-mail addresses for bug reports given in the
> FAQ file and in the help information for bug.report.

Hmm, and neither looks quite right! One would probably want the
address to be in the r-project.org domain (in case we move it away
from Copenhagen). "r-bugs@list.r-project.org", however, is none too
logical and assumes that there's an r-bugs user or an alias in Zurich
which forwards to biostat.dk (there is, it seems). Same thing with
r-bugs@r-project.org, since the Wisconsin machine aliases r-bugs to
r-bugs@lists.r-project.org. 

More logical would be to use r-bugs@r-project.org and have the
forwarding there go to biostat.dk.

Alternatively, it ought to work as r-bugs@bugs.r-project.org, but that
doesn't work whenever a RedHat upgrade blows away the resending rules
in my sendmail.cf... (the program in r-bugs' .forward needs to execute
on a machine that matches the architecture of the binary!)

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk)             FAX: (+45) 35327907
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