From: Robert Barber <robert.barber_at_comcast.net>

Date: Sat 20 Jan 2007 - 19:00:18 GMT

> 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.

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. Received on Sun Jan 21 06:04:25 2007

Date: Sat 20 Jan 2007 - 19:00:18 GMT

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

> sum(A3^2)^.5==1 # here's the part I don't understand

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. Received on Sun Jan 21 06:04:25 2007

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