R devel - Aug 2008 - Truncation error on simply mean & sum function (PR#12515)

Full_Name: Tom Wang
Version: 2.6.2
OS: Linux, Windows
Submission from: (NULL) (61.230.6.228)


I've found an instance:
> a <- c(0.187,-0.019,0.074,-0.06,0.221,-0.079,0.12,0.079,-0.281,-0.242)
> sum(a)
[1] -2.428613e-17

The actual sum is 0 but it reports the wrong answer.

Maybe it is due to the computer truncation error.

On Fri, Aug 8, 2008 at 7:30 AM, <samaya6501@yahoo.com.tw> wrote:
> Full_Name: Tom Wang
> Version: 2.6.2
> OS: Linux, Windows
> Submission from: (NULL) (61.230.6.228)
>
>
> I've found an instance:
>
> > a <-
c(0.187,-0.019,0.074,-0.06,0.221,-0.079,0.12,0.079,-0.281,-0.242)
> > sum(a)
> [1] -2.428613e-17
>
> The actual sum is 0 but it reports the wrong answer.
>
> Maybe it is due to the computer truncation
error.<https://stat.ethz.ch/mailman/listinfo/r-devel>

This is not a bug, but FAQ 7.31.
/Christian

	[[alternative HTML version deleted]]

Not a bug. None of these numbers are exactly representable in binary, so 
you can't expect accuracy of better than machine epsilon.

Please don't report things that aren't bugs to r-bugs.

 	-thomas



On Fri, 8 Aug 2008, samaya6501 at yahoo.com.tw wrote:
> Full_Name: Tom Wang
> Version: 2.6.2
> OS: Linux, Windows
> Submission from: (NULL) (61.230.6.228)
>
>
> I've found an instance:
>
>> a <-
c(0.187,-0.019,0.074,-0.06,0.221,-0.079,0.12,0.079,-0.281,-0.242)
>> sum(a)
> [1] -2.428613e-17
>
> The actual sum is 0 but it reports the wrong answer.
>
> Maybe it is due to the computer truncation error.
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>
Thomas Lumley			Assoc. Professor, Biostatistics
tlumley at u.washington.edu	University of Washington, Seattle