This is the result of how any computer program stores numbers, it's not unique to R. A slightly different question is discussed in R FAQ 7.31 but it applies to your situation. You may also enjoy the R Inferno at www.burns-stat.com/pages/Tutor/R_inferno.pdf
Bryan *********** Bryan Hanson Professor of Chemistry & Biochemistry DePauw University On Sep 11, 2012, at 10:23 AM, Andrea Gonnermann <drel...@googlemail.com> wrote: > 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. ______________________________________________ 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.