Re: [R] one is not one
On Sat, 21 Oct 2006, Philipp Pagel wrote: On Sat, Oct 21, 2006 at 11:04:13AM +0200, Patrick Giraudoux wrote: Which means that actually sum(x) is NOT considered equal to 1... Any idea about what is going wrong? Others have already pointed out the problem and I would like to add a reference to a classical paper on this topic: David Goldberg What Every Computer Scientist Should Know About Floating-Point Arithmetic Computing Surveys, 1991 Reprints can be found in many places online - e.g. here: Yes, and one place is linked from the FAQ entry. -thomas __ R-help@stat.math.ethz.ch 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] one is not one
Folks, I have got a strange behaviour when testing this: sum(x) != 1 let us set x-c(70,134,1,5,0) and transform it in a vector of probabilities x-x/sum(x) One expect sum(x) should be equal to 1, which is apparently the case sum(x) [1] 1 However, when I try to test it I get: if(sum(x) !=1) print(lost) else (OK) [1] lost Which means that actually sum(x) is NOT considered equal to 1... Any idea about what is going wrong? Patrick __ R-help@stat.math.ethz.ch 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.
Re: [R] one is not one
Patrick, the problem arises because computers can't exactly represent real numbers. Try this for your test: if(!all.equal(sum(x),1)) print(lost) else (OK) see FAQ http://cran.r-project.org/doc/FAQ/R-FAQ.html#Why-doesn_0027t-R-think-these-numbers-are-equal_003f I hope that this helps Andrew On Sat, Oct 21, 2006 at 11:04:13AM +0200, Patrick Giraudoux wrote: Folks, I have got a strange behaviour when testing this: sum(x) != 1 let us set x-c(70,134,1,5,0) and transform it in a vector of probabilities x-x/sum(x) One expect sum(x) should be equal to 1, which is apparently the case sum(x) [1] 1 However, when I try to test it I get: if(sum(x) !=1) print(lost) else (OK) [1] lost Which means that actually sum(x) is NOT considered equal to 1... Any idea about what is going wrong? Patrick __ R-help@stat.math.ethz.ch 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. -- Andrew Robinson Department of Mathematics and StatisticsTel: +61-3-8344-9763 University of Melbourne, VIC 3010 Australia Fax: +61-3-8344-4599 http://www.ms.unimelb.edu.au/~andrewpr http://blogs.mbs.edu/fishing-in-the-bay/ __ R-help@stat.math.ethz.ch 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.
Re: [R] one is not one
On Sat, 21 Oct 2006, Patrick Giraudoux wrote: Folks, I have got a strange behaviour when testing this: sum(x) != 1 FAQ 7.31 Why doesn't R think these numbers are equal?: print(sum(x), digits=20) identical(sum(x), 1) all.equal(sum(x), 1) let us set x-c(70,134,1,5,0) and transform it in a vector of probabilities x-x/sum(x) One expect sum(x) should be equal to 1, which is apparently the case sum(x) [1] 1 However, when I try to test it I get: if(sum(x) !=1) print(lost) else (OK) [1] lost Which means that actually sum(x) is NOT considered equal to 1... Any idea about what is going wrong? Patrick __ R-help@stat.math.ethz.ch 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. -- Roger Bivand Economic Geography Section, Department of Economics, Norwegian School of Economics and Business Administration, Helleveien 30, N-5045 Bergen, Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43 e-mail: [EMAIL PROTECTED] __ R-help@stat.math.ethz.ch 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.
Re: [R] one is not one
On Sat, Oct 21, 2006 at 11:04:13AM +0200, Patrick Giraudoux wrote: Which means that actually sum(x) is NOT considered equal to 1... Any idea about what is going wrong? Others have already pointed out the problem and I would like to add a reference to a classical paper on this topic: David Goldberg What Every Computer Scientist Should Know About Floating-Point Arithmetic Computing Surveys, 1991 Reprints can be found in many places online - e.g. here: http://www.physics.ohio-state.edu/~dws/grouplinks/floating_point_math.pdf cu Philipp -- Dr. Philipp PagelTel. +49-8161-71 2131 Dept. of Genome Oriented Bioinformatics Fax. +49-8161-71 2186 Technical University of Munich Science Center Weihenstephan 85350 Freising, Germany and Institute for Bioinformatics / MIPS Tel. +49-89-3187 3675 GSF - National Research Center Fax. +49-89-3187 3585 for Environment and Health Ingolstädter Landstrasse 1 85764 Neuherberg, Germany http://mips.gsf.de/staff/pagel __ R-help@stat.math.ethz.ch 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.
