[R] Question about converting from square roots to decimals and back
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,] 0.000 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. __ 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] Question about converting from square roots to decimals and back
On Sat, 2007-01-20 at 14:00 -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,] 0.000 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. See R FAQ: http://cran.r-project.org/doc/FAQ/R-FAQ.html#Why-doesn_0027t-R-think-these-numbers-are-equal_003f print(sum(A3^2)^.5, 20) [1] 0.99988898 HTH, Marc Schwartz __ 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] Question about converting from square roots to decimals and back
Thank you very much. That was what I needed to know. Bob B. __ 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] Question about converting from square roots to decimals and back
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,] 0.000 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. __ 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.
