Re: [Rd] Numerical error in R (win32) (PR#8909)
Hi
Thanks for the quick reply. However, I am not satisfied, as
> round(3.1500, 1)
[1] 3.1
> round(3.7500, 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: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Peter
Dalgaard
Sent: Monday, May 29, 2006 17:49
To: [EMAIL PROTECTED]
Cc: r-devel@stat.math.ethz.ch; [EMAIL PROTECTED]
Subject: Re: [Rd] Numerical error in R (win32) (PR#8909)
[EMAIL PROTECTED] 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 Øster Farimagsgade 5, Entr.B
c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K
(*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
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Re: [Rd] Numerical error in R (win32) (PR#8909)
Hi
Thanks for the quick reply. However, I am not satisfied, as
> round(3.1500, 1)
[1] 3.1
> round(3.7500, 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: Peter Ehlers [mailto:[EMAIL PROTECTED]
Sent: Monday, May 29, 2006 17:45
To: [EMAIL PROTECTED]
Cc: r-devel@stat.math.ethz.ch
Subject: Re: [Rd] Numerical error in R (win32) (PR#8909)
Did you check the Details section of the help page for round()?
Peter Ehlers
[EMAIL PROTECTED] 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
>
> Regards
> Teckpor
>
>
> [[alternative HTML version deleted]]
>
> __
> R-devel@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
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https://stat.ethz.ch/mailman/listinfo/r-devel
Re: [Rd] Numerical error in R (win32) (PR#8909)
Hi
Thanks for the quick reply. However, I am not satisfied, as
> round(3.1500, 1)
[1] 3.1
> round(3.7500, 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: Duncan Murdoch [mailto:[EMAIL PROTECTED]
Sent: Monday, May 29, 2006 17:41
To: [EMAIL PROTECTED]
Cc: r-devel@stat.math.ethz.ch; [EMAIL PROTECTED]
Subject: Re: [Rd] Numerical error in R (win32) (PR#8909)
On 5/29/2006 12:22 PM, [EMAIL PROTECTED] 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
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