On 08-Jan-10 16:56:25, Paul Evans wrote: > Hi all, > How can I get R to change the default precision value? For example: >> x=0.99999999999999999 >> 1-x > [1] 0 > > Is there a way that I can get a non-zero value using some parameter, > or some package? > many thanks.
The problem here is that, as far as R in concerned, once you have entered x=0.99999999999999999 then x is *exactly* 1. Namely, your x is 1 - 1e-17, and the two things you need to take note of are: .Machine$double.eps # [1] 2.220446e-16 .Machine$double.neg.eps # [1] 1.110223e-16 and the descriptions in ?.Machine which say: "double.eps: the smallest positive floating-point number 'x' such that '1 + x != 1'." "double.neg.eps: a small positive floating-point number 'x' such that '1 - x != 1'. " Both of these (in particular "double.neg.eps") are greater than 1e-17, so your x was stored as 0. I believe there may be packages which can work to greater precision, but I have to leave it to others to describe them (if any). Ted. -------------------------------------------------------------------- E-Mail: (Ted Harding) <ted.hard...@manchester.ac.uk> Fax-to-email: +44 (0)870 094 0861 Date: 08-Jan-10 Time: 17:39:47 ------------------------------ XFMail ------------------------------ ______________________________________________ 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.
