willem vervoort 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 >
Well, this seems not to be what you intended to do, you didn't raise a negative value to a power, but you got the negative of a positive number raised to that power (operator precedence, -51^B is the same as -(51^B) and not the same as (-51)^B...). If you really want to raise a negative value to a fractional power, you may want to tell R to use complex numbers: B <- 47.73092 x <- complex(real=seq(-51,-49,length=10)) x^B [1] 2.117003e+81-2.387323e+81i 1.718701e+81-1.938163e+81i [3] 1.394063e+81-1.572071e+81i 1.129702e+81-1.273954e+81i [5] 9.146212e+80-1.031409e+81i 7.397943e+80-8.342587e+80i [7] 5.978186e+80-6.741541e+80i 4.826284e+80-5.442553e+80i [9] 3.892581e+80-4.389625e+80i 3.136461e+80-3.536955e+80i > Regards, Martin > # 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 > > ______________________________________________ > 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-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.