Hi Robert, does this help?
http://cran.r-project.org/doc/FAQ/R-FAQ.html#Why-doesn_0027t-R-think-these-numbers-are-equal_003f A3<-matrix(nrow=3,c(1/(2^.5),1/(2^.5),0)) sum(A3^2)==1 all.equal(sum(A3^2), 1) Cheers, Andrew On Sat, Jan 20, 2007 at 02:00:18PM -0500, Robert Barber wrote: > Hi, > > I apologize if there is a simple answer to this question that I've > missed. I did search the mailing list but I might not have used the > right keywords. Why does sum(A3^2) give the result of 1, but > sum(A3^2)==1 give the result of FALSE? > > > A3<-matrix(nrow=3,c(1/(2^.5),1/(2^.5),0)) > > A3 > [,1] > [1,] 0.7071068 > [2,] 0.7071068 > [3,] 0.0000000 > > sum(A3^2) > [1] 1 > > sum(A3^2)^.5 > [1] 1 > > sum(A3^2)==1 # here's the part I don't understand > [1] FALSE > > sum(A3^2)^.5==1 # here's the part I don't understand > [1] FALSE > > I realize that it has something to do with the conversion of the square > roots into decimals. But shouldn't it then give me some number other > than 1 as the result for sum(A3^2)? Are there other ways to do this > than what I've tried? I'm trying to confirm that A3 is a unit vector. > > Thank you for your help. > > Bob B. > > ______________________________________________ > [email protected] 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 Statistics Tel: +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/ ______________________________________________ [email protected] 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.
