[R] protential rounding error concern

[Petr Savicky]

On Tue, Jul 31, 2012 at 03:45:14PM -0400, Jie wrote:
> Dear All,
> 
> I am running a r code on 32bit win, involving absolutely small numbers.
> Although I tried sth like the ratio of numers like 10^(-100) and did not
> have issue to get the correct answer,
> but still a little concerned about it.
> Could anyone give some suggestion or have any experience?

Hi.

Numbers of the order 10^(-100) are still relatively far from the lower
limit and are represented with full precision, which is 53 bits.

The smallest number representable in full precision is 2^-1022 = 2.225074e-308
and the smallest representable number (in limited precision) is 2^-1074 =
4.940656e-324.

See 

  http://en.wikipedia.org/wiki/Double_precision_floating-point_format

for more detail.

Hope this helps.

Petr Savicky.