Many,many thanks to all of you and your helpful links! I actually experineced something similar in SAS and my "research" on google was not good enough to figure it out! Well, I may just round the numbers to some digits as proposed So, thank you again for this fast response!! Have a nice day :-) Andrea
On Tue, Sep 11, 2012 at 4:48 PM, PIKAL Petr <petr.pi...@precheza.cz> wrote: > Hi > >> -----Original Message----- >> From: r-help-boun...@r-project.org [mailto:r-help-bounces@r- >> project.org] On Behalf Of Andrea Gonnermann >> Sent: Tuesday, September 11, 2012 4:24 PM >> 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? > > Because you are probably using computer. Some fractional decimal numbers > cannot be expressed as binary finite precision numbers. You can round your > result to get 0. BTW it is covered in FAQ 7.31 (I believe) > > Regards > Petr > >> >> 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.
