From: Berwin A Turlach <berwin_at_maths.uwa.edu.au>

Date: Tue, 07 Oct 2008 19:48:27 +0800

[1] 0.5682923 0.5956102 0.6229280 0.6502459 0.6775638 0.7048816 [7] 0.7321995 0.7595174 0.7868352 0.8141531 0.8414710

[1] 0.2731787 0.2731787 0.2731787 0.2731787 0.2731787 0.2731787 [7] 0.2731787 0.2731787 0.2731787 0.2731787 0.2731787

[1] 0 0 0 0 0 0 0 0 0 0 0

R> splfun( seq(0,1, 0.1), deriv=3 )

[1] 0 0 0 0 0 0 0 0 0 0 0

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Received on Tue 07 Oct 2008 - 11:56:21 GMT

Date: Tue, 07 Oct 2008 19:48:27 +0800

On Tue, 7 Oct 2008 19:31:03 +0800

Berwin A Turlach <berwin_at_maths.uwa.edu.au> wrote:

> The attached patch (against the current SVN version of R) implements

*> the latter strategy. With this patch applied, "make check
**> FORCE=FORCE" passes on my machine. The version of R that is build
**> seems to give the correct answer in your example:
*

Perhaps I should have thought a bit more about this. For a natural spline c[1] is zero, and d[1] is typically not but for evaluations left of the first knot it should be taken as zero. So the attached patch solves the problem in what some might consider a more elegant manner. :)

With the patch "make check FORCE=FORCE" works on my machine and it also solves your example:

R> x <- 1:10 R> y <- sin(x) R> R> splfun <- splinefun(x,y, method='natural') R> R> # these should be linear (and are) R> splfun( seq(0,1, 0.1) )

[1] 0.5682923 0.5956102 0.6229280 0.6502459 0.6775638 0.7048816 [7] 0.7321995 0.7595174 0.7868352 0.8141531 0.8414710

R> R> # these should all be the same R> splfun( seq(0,1, 0.1), deriv=1 )

[1] 0.2731787 0.2731787 0.2731787 0.2731787 0.2731787 0.2731787 [7] 0.2731787 0.2731787 0.2731787 0.2731787 0.2731787

R> R> # these should all be 0 R> splfun( seq(0,1, 0.1), deriv=2 )

[1] 0 0 0 0 0 0 0 0 0 0 0

R> splfun( seq(0,1, 0.1), deriv=3 )

[1] 0 0 0 0 0 0 0 0 0 0 0

**HTH.
**
Cheers,

Berwin

- Full address =============================
Berwin A Turlach Tel.: +65 6516 4416 (secr)
Dept of Statistics and Applied Probability +65 6516 6650 (self)
Faculty of Science FAX : +65 6872 3919
National University of Singapore
6 Science Drive 2, Blk S16, Level 7 e-mail: statba_at_nus.edu.sg
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