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

**Peter Dalgaard BSA
**
p.dalgaard@biostat.ku.dk

*04 Sep 2000 14:28:37 +0200*

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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