Numerical error in R (win32) (PR#8909)

Hi

	Thanks for the quick reply. However, I am not satisfied, as

round(3.15000000, 1)

[1] 3.1

round(3.75000000, 1)

[1] 3.8

	I think the problem is really more of an error in the rounding off
algorithm than finite precision.

Thanks
Teckpor

-----Original Message-----
From: pd at pubhealth.ku.dk [mailto:pd at pubhealth.ku.dk] On Behalf Of Peter
Dalgaard
Sent: Monday, May 29, 2006 17:49
To: teck.lim at imperial.ac.uk
Cc: r-devel at stat.math.ethz.ch; R-bugs at biostat.ku.dk
Subject: Re: [Rd] Numerical error in R (win32) (PR#8909)

teck.lim at imperial.ac.uk writes:

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

According to what? Remember that we're dealing with finite precision binary
arithmetic here:

 (3.15 - 3.1)<.05

[1] TRUE

 abs(3.15 - 3.2)>.05

[1] TRUE

See also FAQ 7.31.

Regards
Teckpor

O__  ---- Peter Dalgaard             ?ster Farimagsgade 5, Entr.B
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