Your numbers are 70 bits long, R double precision numbers are 53 bits long. You need Rmpfr to get the higher precision.
> log(569936821221962380720, 2) [1] 68.94936 > print(569936821221962380720, digits=22) [1] 569936821221962350592 > library(Rmpfr) > mpfr("569936821221962380720", 70) 1 'mpfr' number of precision 70 bits [1] 569936821221962380720 > > mpfr("569936821221962380720", 210)^3 + (mpfr("-569936821113563493509", > 210))^3 + (mpfr("-472715493453327032", 210))^3 1 'mpfr' number of precision 210 bits [1] 3 See FAQ 7.31 and the help files for Rmpfr Rich On Tue, Sep 17, 2019 at 6:13 PM Duncan Murdoch <murdoch.dun...@gmail.com> wrote: > > On 17/09/2019 6:02 p.m., Martin Møller Skarbiniks Pedersen wrote: > > Hi, > > I don't understand why R computes this wrong. > > This is pretty well documented. R uses double precision floating point > values for these expressions, which have about 15 digit precision. I > believe for whole numbers Python uses variable size integer values, so > should get integer calculations exactly right. > > You can also tell R to use exact 32 bit integer calculations, but your > values are too big for that, so it wouldn't work in this example. > > > > I know I can use gmp and > > R will do it correctly. > > > > $ echo '569936821221962380720^3 + (-569936821113563493509)^3 + > > (-472715493453327032)^3' | Rscript - [1] -4.373553e+46 > > Correct answer is 3 and Python can do it: > > > > $ echo > > 'pow(569936821221962380720,3)+pow(-569936821113563493509,3)+pow(-472715493453327032,3)'|python3 > > 3 > > > > [[alternative HTML version deleted]] > > Please don't post HTML to the list -- it's a plain text list. That's > also pretty well documented. > > Duncan Murdoch > > ______________________________________________ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > 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 -- To UNSUBSCRIBE and more, see 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.