[R] Precision in R

Marc Schwartz MSchwartz at MedAnalytics.com
Tue Jul 20 19:50:55 CEST 2004

On Tue, 2004-07-20 at 12:13, Duncan Murdoch wrote:
> On Tue, 20 Jul 2004 11:55:32 -0400, adelmaas at musc.edu wrote :
> >Does anyone know 
> >where I can find specifications for R's type double?  
> As far as I know, all platforms use the IEEE-754 standard double
> precision numbers.  Google will give you a description; here's one:
> http://research.microsoft.com/~hollasch/cgindex/coding/ieeefloat.html
> This isn't relevant to your question, but I found the history of the
> development of the standard interesting:
> http://http.cs.berkeley.edu/~wkahan/ieee754status/754story.html
> Duncan Murdoch


The standard is there, but not all applications stick to it faithfully.
A good example being how certain <cough> spreadsheets <\cough> deal with
numbers "close to zero".

For example, Excel will round numbers "close to zero" to zero. You may
recall this thread from last year covered this topic


More information on Excel's varied compliance with the IEEE 754 standard
is available here


The official IEEE 754 page is at http://grouper.ieee.org/groups/754/ and
there are some good reading materials and FAQ's there.

This above is beyond the scope of SAS in particular, but I suspect that
the difference that Aaron is experiencing, as Andy has noted, is
methodologic and not precision related.

Aaron, one other source for information on the precision of R on your
particular machine is the use of .Machine, which will provide you with a
list of specifications. See ?.Machine for additional information here.


Marc Schwartz

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