[Rd] numerical issue in contour.default?

[Prof Brian Ripley]

On 13/09/2013 15:14, Duncan Murdoch wrote:
> On 13/09/2013 10:01 AM, Thomas Petzoldt wrote:
>> Dear R developers,
>>
>> I found a small issue while plotting contours of data containing both
>> "usual" and "very small" numbers. It appeared with both R 3.0.1 and
>> R-Devel on Windows, and I could reproduce it on Linux. Would it be
>> possible to solve this before the upcoming release?
>
> I don't see the error in 32 bits, but I do see it in 64 bits.  I think
> it's really unlikely this will be fixed before 3.0.2, unless you send a
> well tested patch in the next few days.  Code freeze is on Wednesday.

And not even then: we would not have time to do sufficiently extensive 
checking.

Reporting to bugs.r-project.org with a patch would get the process rolling.

>
> Duncan Murdoch
>>
>> Thanks a lot for developing this great software!
>>
>> Thomas
>>
>>
>> Example:
>> ########
>>
>>
>> set.seed(357)
>> z1 <- matrix(runif(100, -1e-180, 1e-180), nrow = 10)
>> contour(z1)    # ok
>>
>> z2 <- matrix(c(runif(50, -1, 1), runif(50, -1e-180, 1e-180)), nrow = 10)
>> contour(z2)   # Error in contour.default(z) : k != 2 or 4
>>
>> contour(z2 * 1e20)        # 20 worked, 19 produced error
>> contour(round(z2, 179))   # rounding to 179 digits works but not 180
>>
>>
>> > sessionInfo()
>> R Under development (unstable) (2013-09-11 r63910)
>> Platform: x86_64-w64-mingw32/x64 (64-bit)
>>
>> locale:
>> [1] LC_COLLATE=German_Germany.1252  LC_CTYPE=German_Germany.1252
>> [3] LC_MONETARY=German_Germany.1252 LC_NUMERIC=C
>> [5] LC_TIME=German_Germany.1252
>>
>> attached base packages:
>> [1] stats     graphics  grDevices utils     datasets  methods   base
>>
>>
>>
>>
>>
>
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-- 
Brian D. Ripley,                  ripley at 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