on 07/01/2008 01:15 PM [EMAIL PROTECTED] wrote:
Can someone please enlighten me as to why the following happens?
-2.7^8.6
[1] -5125.407
p<- -2.7 q<- 8.6 p^q
[1] NaN
R seems perfectly able to calculate -2.7^8.6, but fails when
the exact same values are assigned to variables and then the
computation is repeated. Thanks in advance for any suggetsions. Kris.
You are not seeing what you think you are seeing in the first result.
> -2.7^8.6
[1] -5125.407
is parsed in the same way as:
> -(2.7^8.6)
[1] -5125.407
In other words, it is parsed as:
> 2.7^8.6
[1] 5125.407
and then negated.
If you were to 'properly' define the precedence of operation, you would use:
> (-2.7)^8.6
[1] NaN
which is the same result you get when you use the vectors.
See R FAQ 7.33 Why are powers of negative numbers wrong?:
http://cran.r-project.org/doc/FAQ/R-FAQ.html#Why-are-powers-of-negative-numbers-wrong_003f
HTH,
Marc Schwartz
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