R help - Oct 2009 - possible to increase precision

I would like to increase the precision/accuracy of R.  That is, I'm  
dealing with numbers exceedingly close to 1, and I would like to  
increase the number of significant digits used in computation.  In  
matlab, you can use vpa() to accomplish this. I'm wondering if there's  
an equivalent or a workaround in R.

Greg

I would like to increase the precision/accuracy of R.  That is, I'm  
dealing with numbers exceedingly close to 1, and I would like to  
increase the number of significant digits used in computation.  In  
matlab, you can use vpa() to accomplish this. I'm wondering if there's  
an equivalent or a workaround in R.

Greg

Hi Greg,
Others on this list are much more knowledgeable than I am, and I'm
sure they  will correct me if I'm wrong.

My understanding is that R uses double precision (see
http://en.wikipedia.org/wiki/Double_precision_floating-point_format),
which has the following implication:
> x <- c(1,2,3)/10^308
> x*10^308
[1] 1 2 3
> x <- c(1,2,3)/10^309
> x*10^309
[1] NaN NaN NaN

among others. See

RSiteSearch("floating point")

for other additional implications. I think you're out of luck it you
need to work with values smaller than 1*10^308.

-Ista

On Fri, Oct 30, 2009 at 5:04 PM, Greg Michaelson <gmichaelson at me.com>
wrote:
> I would like to increase the precision/accuracy of R. ?That is, I'm
dealing
> with numbers exceedingly close to 1, and I would like to increase the
number
> of significant digits used in computation. ?In matlab, you can use vpa() to
> accomplish this. I'm wondering if there's an equivalent or a
workaround in
> R.
>
> Greg
>
> ______________________________________________
> R-help at 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.
>


-- 
Ista Zahn
Graduate student
University of Rochester
Department of Clinical and Social Psychology
http://yourpsyche.org

On 30/10/2009 5:04 PM, Greg Michaelson wrote:
> I would like to increase the precision/accuracy of R.  That is, I'm  
> dealing with numbers exceedingly close to 1, and I would like to  
> increase the number of significant digits used in computation.  In  
> matlab, you can use vpa() to accomplish this. I'm wondering if
there's
> an equivalent or a workaround in R.
There's a package for extra precision, but you'd probably be better off 
just working with log(x).  That will give you about 300+ digits of 
precision near 1, i.e. log(1 + epsilon) is representable accurately down 
to epsilon=10^(-300).

Duncan Murdoch