[Rd] Numerical error in R (win32) (PR#8909)

Duncan Murdoch
2006-05-29T16:40:51Z

On 5/29/2006 12:22 PM, teck.lim at imperial.ac.uk wrote:
> Hi
>     I had observed the following problem in R (also C, Matlab, and Python).
> sprintf('%1.2g\n', 3.15)
> give 3.1 instead of 3.2 whereas an input of 3.75 gives 3.8.
> Java's System.out.printf is ok though.
>
>> round(3.75,1)
> [1] 3.8
>> round(3.15,1)
> [1] 3.1
>
> Similar outcome with sprintf in R.
>
>
> However, the right answer should be 3.2

This is not a bug.  There is no way to represent 3.15 exactly in double
precision, so it is hard to predict whether it will round up or down.
Apparently on the machine you were using it is represented as a number
slightly less than 3.15, which rounds down.

Duncan Murdoch