Patrick Aboyoun wrote: > I've stumbled across an issue with aggregate.ts that either is due to a > misuse of %/% or something deeper relating to numerical precision on > Windows. The test code is > > x <- rep(6:10, 1:5) > as.vector(aggregate(as.ts(x), FUN = mean, ndeltat = 5)) > > On Linux and Mac I get the correct answer > > > x <- rep(6:10, 1:5) > > as.vector(aggregate(as.ts(x), FUN = mean, ndeltat = 5) > [1] 7.2 8.8 10.0 > > > sessionInfo() > R version 2.11.0 RC (2010-04-18 r51771) > i386-apple-darwin9.8.0 > > locale: > [1] en_US.UTF-8/en_US.UTF-8/C/C/en_US.UTF-8/en_US.UTF-8 > > attached base packages: > [1] stats graphics grDevices utils datasets methods base > > > and on Windows I get an incorrect answer > > > x <- rep(6:10, 1:5) > > as.vector(aggregate(as.ts(x), FUN = mean, ndeltat = 5)) > [1] 7.0 8.5 9.5 > > > sessionInfo() > R version 2.11.0 beta (2010-04-11 r51685) > i386-pc-mingw32 > > locale: > [1] LC_COLLATE=English_United States.1252 > [2] LC_CTYPE=English_United States.1252 > [3] LC_MONETARY=English_United States.1252 > [4] LC_NUMERIC=C > [5] LC_TIME=English_United States.1252 > > attached base packages: > [1] stats graphics grDevices utils datasets methods base > > > Walking through the aggregate.ts code I found this difference is due to > what 1 %/% 0.2 produces on the different platforms. > > On Mac and Linux I get > > > 1 %/% 0.2 > [1] 5 > > and on Windows I get > > > 1 %/% 0.2 > [1] 4 > > > I don't know if %/% supports floating point operands so I'm not sure how > to report this issue, but here it is anyway.
It's not as straightforward as that. I get 4 on one (32 bit) Linux, and 5 on another (64 bit). Based on samples of size one, I wouldn't want to conjecture that "bitness" is the root cause, but it is probably not the OS per se, rather the CPU or compiler version. It is even more insidious: I see on the SAME system > 1%/%0.2 [1] 4 > 1/0.2==5 [1] TRUE so it isn't just the usual precision issue. Of course, exact calculations with floating-point numbers is "unsafe at any speed", but this is quite peculiar. Presumably, it comes about because of intermediate storage in an extended precision register. -- Peter Dalgaard Center for Statistics, Copenhagen Business School Phone: (+45)38153501 Email: pd....@cbs.dk Priv: pda...@gmail.com ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
