Not directly related to what you said below, but might I suggest that for numerical work all.equal() might be a little more robust in a computationally heavy implementation.
x = c(0.812672,0.916541,0.797810) #dont' call variables c -- just a bad idea y = x[1]+x[2]+x[3] > sum(x) ==y [1] FALSE > identical(sum(x),y) [1] FALSE > all.equal(sum(x),y) [1] TRUE But yeah, it's just a floating point thing. Michael Weylandt PS -- Just so no one else has to say it: obligatory mention of R FAQ 7.31: http://cran.r-project.org/doc/FAQ/R-FAQ.html#Why-doesn_0027t-R-think-these-numbers-are-equal_003f On Tue, Aug 23, 2011 at 3:17 PM, Daniel Lai <dan...@bccrc.ca> wrote: > Greetings all, > > I'm porting an algorithm from MATLAB to R, and noticed some minor > discrepancies in small decimal values using rowSums and colSums which are > exacerbated after heavy iteration and log space transformation. This was > rather perplexing as both programs claimed and appeared to use the IEEE 754 > standard for floating point arithmetic (confirmed with manual basic > operations). After some tracing and testing, I've managed to isolated a > minimal working example as follows: > > a = 0.812672 > b = 0.916541 > c = 0.797810 > sum(c(a, b, c)) == (a + b + c) > [1] FALSE > > Should I attribute this to the woes of working with floating point numbers > and accept it? i.e. > > sprintf("%.30f", sum(c(a, b, c))) > [1] "2.**527022999999999797182681504637**" > sprintf("%.30f", (a + b + c)) > [1] "2.**527023000000000241271891354700**" > > Change the OS or version I'm using? > > MAC OSX 10.5.8: > sessionInfo() > R version 2.13.1 (2011-07-08) > Platform: i386-apple-darwin9.8.0/i386 (32-bit) > attached base packages: > [1] stats graphics grDevices utils datasets methods base > > Linux 2.6.34: > R version 2.12.0 (2010-10-15) > Platform: x86_64-unknown-linux-gnu (64-bit) > attached base packages: > [1] stats graphics grDevices utils datasets methods base > > Or report this as a bug? > > Thanks, > Daniel > > ______________________________**________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/**listinfo/r-help<https://stat.ethz.ch/mailman/listinfo/r-help> > PLEASE do read the posting guide http://www.R-project.org/** > posting-guide.html <http://www.R-project.org/posting-guide.html> > and provide commented, minimal, self-contained, reproducible code. > [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
