On 15/10/2013 14:00, Rosenberger George wrote:
Dear R Developers
I'm using the great randomForest package (4.6-7) for many projects and recently
stumbled upon a problem when I wrote unit tests for one of my projects:
On Windows, there are small numeric deviations when using the 32- / 64-bit
version of R, which doesn't seem to be a problem on Linux or Mac.
R64 on Windows produces the same results as R64/R32 on Linux or Mac:
set.seed(131)
importance(randomForest(Species ~ ., data=iris))
MeanDecreaseGini
Sepal.Length 9.452470
Sepal.Width 2.037092
Petal.Length 43.603071
Petal.Width 44.116904
R32 on Windows produces the following:
set.seed(131)
importance(randomForest(Species ~ ., data=iris))
MeanDecreaseGini
Sepal.Length 9.433986
Sepal.Width 2.249871
Petal.Length 43.594159
Petal.Width 43.941870
Is there a reason why this is different for the Windows builds? Are the
compilers on Windows doing different things for 32- / 64-bit builds than the
ones on Linux or Mac?
Yes, no (but these are not R issues).
There are bigger differences in the OS's equivalent of libm on Windows.
You did not tell us what CPUs your compilers targeted on Linux and OS
X (sic), but generally they assume more than the i386 assumed on 32-bit
Windows by Microsoft. OTOH, all x86_64 OSes, including Windows, can
assume more as all such CPUs have post-i686 features. Remember Windows
XP is still supported, and that was released in 2001.
Based on much wider experience than you give (e.g. reference results
from R itself and recommended packages), deviations from x86_64 results
are increasingly likely on OS X, i686 Linux and then i386 Windows.
--
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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