See R Faq (http://cran.r-project.org/doc/FAQ/R-FAQ.html) with particular attention to FAQs 7.31 and 9.1 paragraph 3.
Essentially, computational precision is finite. S Ellison > -----Original Message----- > From: r-help-boun...@r-project.org > [mailto:r-help-boun...@r-project.org] On Behalf Of Andrea Gonnermann > Sent: 11 September 2012 15:24 > To: r-help@r-project.org > Subject: [R] R calculates small numbers, where the result > should be zero > > Hi all, > > my problem is that R does wrong calculations, when the result > should be zero. > I have the following code: > > RD_Var1 <- ((0.1*(1-0.1))/100)+((0.2*(1-0.2))/100) > RD_Var2 <- ((0.1*(1-0.1))/100)+((0.2*(1-0.2))/100) > RD_1 <- 0.1-0.2 > RD_1 > RD_2 <- 0.1-0.2 > FEM_Eff_RD <- > ((1/RD_Var1)*RD_1+(1/RD_Var2)*RD_2)/(1/RD_Var1+1/RD_Var2) > Q_RD <- > 1/RD_Var1*((RD_1-FEM_Eff_RD)^2)+1/RD_Var2*((RD_2-FEM_Eff_RD)^2) > Q_RD > My result is: > 1.540744e-31 > When I put the calculated numbers directly into the last > formula, I get zero, which is the correct answer: > Q_RD <- 1/0.0025*((-0.1--0.1)^2)+1/0.0025*((-0.1--0.1)^2) > > Why does R calculate the other number instead of zero? > > Thank you very much for your help! > > ______________________________________________ > 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. > ******************************************************************* This email and any attachments are confidential. Any use...{{dropped:8}} ______________________________________________ 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.
