On Mon, 5 Jul 2004, Laura Holt wrote:
> What precision is R, please? 64 bit?
Your question lacks precision :)
R uses the underlying double precision floating-point arithmetic of the OS
it is running on. On all currrent platforms that we know of, that is
IEC60566 arithmetic, with an (implicit) 53-bit mantissa.
So floating-point operations have double precision, usually with around 53
bits of accuracy.
> Where would I find that out typically, please?
Type ?.Machine, then print(.Machine).
One complication on machines with extended-precision registers (and since
that includes the ix86 family, that is most of them) is that some
calculations are done with a 64-bit mantissa and finally stored with a
53-bit mantissa. Those may turn out to be more accurate than your expect
(which makes measuring accuracy difficult).
--
Brian D. Ripley, ripley at stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595