bug in spline()? (PR#653)
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 -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-devel mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-devel-request@stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._