First of all, read FAQ 7.31 to understand that 1/3 is not representable in floating point. Also a^b is actually exp(log(a) * b) and log(-8) is not valid (NaN).
You expression is not really taking the cube root; it is taking values to the 1/3 power. If you want to cube root function, then try: > cubeRoot <- function(x) sign(x) * exp(log(abs(x)) / 3) > cubeRoot(8) [1] 2 > cubeRoot(-8) [1] -2 > > On Sat, Jul 18, 2009 at 6:04 PM, Dave DeBarr<dave.deb...@microsoft.com> wrote: > Why does the expression "(-8)^(1/3)" return NaN, instead of -2? > > This is not answered by > http://cran.r-project.org/doc/FAQ/R-FAQ.html#Why-are-powers-of-negative-numbers-wrong_003f > > Thanks, > Dave > > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@r-project.org 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. > -- Jim Holtman Cincinnati, OH +1 513 646 9390 What is the problem that you are trying to solve? ______________________________________________ R-help@r-project.org 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.
