[R] Machine accurancy.

[ripley@stats.ox.ac.uk]

On Sun, 9 Jun 2002, Kenneth Cabrera wrote:

> Hi, R-users and developers!
>
> I want to know if it is possible to modify some numeric precision on a
> windows based machine.
> I mean, .Machine() function give me some limits of precision based on my
> machine and OS, but
> I would like to know if I can modify those characteristics from R.
> May I change some C++ library by other and recompile R?

No. And R does not use any C++. Most of the characteristics are of the
ix86 chip and IEEE754 arithmetic.  You might be able to use
64-bit-mantissa doubles, if you could find a runtime (`libc') that
supported that.

> Is it possible to use some specific processor characteristics?
> I'm using R in a W2K O.S, and with an Intel PIII, machine.
> Are those characteristics R better on a LINUX O.S. machine on the same
> PIII processor?

No, they are the same.

> Is it better to use R in the LINUX platform than in W2K with regards
> this machine precision?

Not really.  The Linux runtime might be a little more accurate.

Why do you want to do this?  R's precision is quite sufficient for almost
all scientific purposes, if used correctly.

> Thank you very much for your help
>
> Kenneth
>
> double.eps             2.220446e-16
> double.neg.eps      1.110223e-16
> double.xmin           2.225074e-308
> double.xmax          1.797693e+308
> double.base           2
> double.digits          53
> double.rounding     5
> double.guard         0
> double.ulp.digits    -52
> double.neg.ulp.digits -53
> double.exponent      11
> double.min.exp      -1022
> double.max.exp       1024
> integer.max              2147483647
> sizeof.long               4
> sizeof.longlong         8
> sizeof.longdouble     12
>
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-- 
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 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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