This is standard behaviour for a floating-point computational system like R. You might like to take a look at this blog post for a backgrounder on floating-point arithmetic in R.
http://blog.revolutionanalytics.com/2009/03/when-is-a-zero-not-a-zero.html # David Smith On Mon, Jun 18, 2012 at 2:26 PM, whf1984911 <whf1984...@yahoo.com.cn> wrote: > > Hi, > > This problems has bothered me for the lase couple of hours. > > > 1e-100==0 > [1] FALSE > > (1-1e-100)==1 > [1] TRUE > > How can I tell R that 1-1e-100 does not equal to 1, actually, I found out > that > > (1-1e-16)==1 > [1] FALSE > > (1-1e-17)==1 > [1] TRUE > > The reason I care about this is that I was try to use qnorm() in my code, > for example, > > > qnorm(1e-100) > [1] -21.27345 > > and if I want to find qnorm(x) where x is very close to 1, say x=1-1e-100, > then you would think using > qnorm(1-x, lower.tail=F) would give me something other than INF, but that > does not work since R would recognize x==1 in this case and therefore, > 1-x==0, so qnorm(1-x, lower.tail=F) will give me INF which is what I try > to > avoid in my code. > > How could get around this, any suggestions? > > Thanks, > Haifeng Wu > Graduate Student > University of South Carolina -- David M Smith <da...@revolutionanalytics.com> VP of Marketing, Revolution Analytics http://blog.revolutionanalytics.com Tel: +1 (650) 646-9523 (Palo Alto, CA, USA) Twitter: @revodavid ______________________________________________ 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.
