[Rd] bug (PR#13570)

[Peter Dalgaard]

Prof Brian Ripley wrote:
> 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.)

The code itself has

    if (!match(degree, 0:2, 0))
        stop("'degree' must be 0, 1 or 2")

though. "Local fitting of a constant" essentially becomes kernel
smoothing, right?


> 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.dalgaard at biostat.ku.dk> wrote:
>>>
>>>> rhafen at 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
>>>
>>> ______________________________________________
>>> R-devel at r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>
>>
>> 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
>>
>> ______________________________________________
>> R-devel at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>
> 


-- 
   O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
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