[R] exactly representable numbers

From: Robin Hankin <r.hankin_at_noc.soton.ac.uk>
Date: Mon 11 Sep 2006 - 08:52:03 GMT


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?

--
Robin Hankin
Uncertainty Analyst
National Oceanography Centre, Southampton
European Way, Southampton SO14 3ZH, UK
  tel  023-8059-7743

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Received on Mon Sep 11 18:59:20 2006

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