Check out sum.exact and cumsum.exact in the caTools package. > library(caTools) Loading required package: bitops > x <- 1/(12:14) > sum(x) - cumsum(x)[3] [1] 2.775558e-17 > sum.exact(x) - cumsum.exact(x)[3] [1] 0
On Tue, Feb 17, 2009 at 5:12 PM, Stavros Macrakis <macra...@alum.mit.edu> wrote: > I recently traced a bug of mine to the fact that cumsum(s)[length(s)] > is not always exactly equal to sum(s). > > For example, > > x<-1/(12:14) > sum(x) - cumsum(x)[3] => 2.8e-17 > > Floating-point addition is of course not exact, and in particular is > not associative, so there are various possible reasons for this. > Perhaps sum uses clever summing tricks to get more accurate results? > In some quick experiments, it does seem to get more accurate results > than cumsum. > > It might be worth documenting. > > -s > > ______________________________________________ > 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. > ______________________________________________ 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.
