Anthony Landrevie wrote:
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?
Depends, e.g. you mightg want to see that the result is only -5.684342e-14 off, hence not identical() to, but all.equal() with what you expected.
Why is the difference not equal to zero?
Floating point calculations on a digital computer are involved...
Uwe Ligges
I am using R 2.0.1 under Windows XP.
Regards,
Anthony Landrevie
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