On 8/30/07, Gustaf Rydevik <[EMAIL PROTECTED]> wrote: > On 8/30/07, willem vervoort <[EMAIL PROTECTED]> wrote: > > Dear all, > > I am struggling to understand this. > > > > What happens when you raise a negative value to a power and the result > > is a very large number? > > > > B > > [1] 47.73092 > > > > > -51^B > > [1] -3.190824e+81 > > > > # seems fine > > # now this: > > > x <- seq(-51,-49,length=100) > > > > > x^B > > [1] NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN > > <snip> > > > is.numeric(x^B) > > [1] TRUE > > > is.real(x^B) > > [1] TRUE > > > is.infinite(x^B) > > [1] FALSE FALSE FALSE FALSE FALSE > > > > I am lost, I checked the R mailing help, but could not find anything > > directly. I loaded package Brobdingnag and tried: > > as.brob(x^B) > > [1] NAexp(NaN) NAexp(NaN) NAexp(NaN) NAexp(NaN) NAexp(NaN) > > > as.brob(x)^B > > [1] NAexp(187.67) NAexp(187.65) NAexp(187.63) NAexp(187.61) > > > > I guess I must be misunderstanding something fundamental. > > > > Any clues would be really appreciated. > > Willem > > > > non-integer exponents of non-positive values are not defined, thus the NaN. > > > -1^2.5 > [1] -1 > > (-1)^2.5 > [1] NaN > > > > Best, > > Gustaf >
To modify, that is if you are working with reals. > x [1] -1 > x^(1/2) [1] NaN > class(x)<-"complex" > x^(1/2) [1] 0+1i > x<--51 > x^47.7 [1] NaN > class(x)<-"complex" > x^47.7 [1] 1.660795e+81-2.285889e+81i > Best, Gustaf -- Gustaf Rydevik, M.Sci. tel: +46(0)703 051 451 address:Essingetorget 40,112 66 Stockholm, SE skype:gustaf_rydevik ______________________________________________ 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.