Hello,
 
I am trying to test the precision of R on datasets from The Statistical Reference Datasets Project http://www.itl.nist.gov/div898/strd/index.html and I don't manage to understand how R is storing its results.
 
For example, I calculate a mean on the michelso dataset (100 values) and find:
 
> m=mean(michel)
> m
      V1 
299.8524 
> print(m,digits=15)
      V1 
299.8524 

> print(m,digits=22)
                V1 
299.85239999999993 

 
The certified value of the mean is 299.85240, so I try
 
 
> print(m-299.8524)
           V1 
-5.684342e-14 
 
> print(m-299.8524,digits=15)
                   V1 
-5.68434188608080e-14 

Does it have a sens to print with more than 15 signifiant digits?
Why is the difference not equal to zero?
 
I am using R 2.0.1 under Windows XP.
 
Regards,
 
Anthony Landrevie 

		
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