Robin Hankin said the following on 9/11/2006 3:52 AM: > Hi > > Given a real number x, I want to know how accurately R can represent > numbers near x. > > In particular, I want to know the infinum of exactly representable > numbers greater than x, and the supremum of exactly representable > numbers > less than x. And then the interesting thing is the difference > between these two. > > > I have a little function that does some of this: > > > f <- function(x,FAC=1.1){ > delta <- x > while(x+delta > x){ > delta <- delta/FAC > } > return(delta*FAC) > } > > But this can't be optimal. > > Is there a better way? > > >
I believe this is what .Machine$double.eps is. From ?.Machine double.eps: the smallest positive floating-point number 'x' such that '1 + x != 1'. It equals 'base^ulp.digits' if either 'base' is 2 or 'rounding' is 0; otherwise, it is '(base^ulp.digits) / 2'. See also .Machine$double.neg.eps. Is this what you need? --sundar ______________________________________________ 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.