Undortunately the example is random, so not really reproducible (and I
see nothing wrong on my Mac). However, Linux valgrind on R-devel is
showing a problem:
==3973== Conditional jump or move depends on uninitialised value(s)
==3973== at 0xD76017B: ehg141_ (loessf.f:532)
==3973== by 0xD761600: lowesa_ (loessf.f:769)
==3973== by 0xD736E47: loess_raw (loessc.c:117)
(The uninitiialized value is in someone else's code and I suspect it
was either never intended to work or never tested.) No essential
change has been made to the loess code for many years.
I would not have read the documentation to say that degree = 0 was a
reasonable value. It is not to my mind 'a polynomial surface', and
loess() is described as a 'local regression' for degree 1 or 2 in
the reference. So unless anyone wants to bury their heads in that
code I think a perfectly adequate fix would be to disallow degree = 0.
(I vaguely recall debating allowing in the code ca 10 years ago.)
On Thu, 5 Mar 2009, Uwe Ligges wrote:
Berwin A Turlach wrote:
G'day Peter,
On Thu, 05 Mar 2009 09:09:27 +0100
Peter Dalgaard <p.dalga...@biostat.ku.dk> wrote:
rha...@stat.purdue.edu wrote:
<<insert bug report here>>
This is a CRITICAL bug!!! I have verified it in R 2.8.1 for mac
and for windows. The problem is with loess degree=0 smoothing.
For example, try the following:
x <- 1:100
y <- rnorm(100)
plot(x, y)
lines(predict(loess(y ~ x, degree=0, span=0.5)))
This is obviously wrong.
Obvious? How? I don't see anything particularly odd (on Linux).
Neither did I on linux; but the OP mentioned mac and windows.
On windows, on running that code, the lines() command added a lot of
vertical lines; most spanning the complete window but some only part.
Executing the code a second time (or in steps) gave sensible
results.
My guess would be that some memory is not correctly allocated or
initialised. Or is it something like an object with storage mode
"integer" being passed to a double? But then, why doesn't it show on
linux?
Happy bug hunting. If my guess is correct, then I have no idea how to
track down such things under windows.....
Cheers,
Berwin
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Please can you folks try under R-devel (to be R-2.9.0 in a couple of weeks)
and report if you still see it. I do not under R-devel (but do under
R-release), so my guess is that something called by loess() has been fixed in
the meantime.
Moreover it is not the plot stuff that was wrong under R-2.8.1 (release) but
the loess computations.
Uwe Ligges
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--
Brian D. Ripley, rip...@stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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