[R] Question about converting from square roots to decimals and back
Robert Barber
robert.barber at comcast.net
Sat Jan 20 20:00:18 CET 2007
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.
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