Re: [Rd] Truncation error on simply mean & sum function (PR#12515)

From: Thomas Lumley <tlumley_at_u.washington.edu>
Date: Fri, 08 Aug 2008 09:41:37 -0700 (PDT)

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.
>
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>

Thomas Lumley			Assoc. Professor, Biostatistics
tlumley_at_u.washington.edu	University of Washington, Seattle

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