[R] Problem about zero

[Gabor Grothendieck]

On Tue, Jun 15, 2010 at 6:00 PM, Yen Lee <b88207001 at ntu.edu.tw> wrote:
> Hello, everyone,
>
> There's a problem about zero in R and I really need your help.
>
>
>
> I have a vector shown as x=c(0.1819711,0.4811463,0.1935151,0.1433675),
>
> The sum of this vector is shown as 1 in R, but when I type 1-sum(x), the
> value is not zero, but -2.220446e-16.
>
> I can accept that this value is quite small and could be seen as zero, but
> there would be a problem when it's not really zero but a negative value in
> my algorithm.
>
>
>
> Therefore I would like to know that how could it be avoid.
>
> One way I think is to define the value 1-sum(x) as zero when it is smaller
> than a particular value, but the particular value is not be set yet.
>
> I would like to know more about the definition of the shown zero in R.
>

As others have pointed out please read the R FAQ.

Actually on my machine: Windows Vista running C2D BLAS, "R version
2.11.1 Patched (2010-05-31 r52167)"
I do get zero:

> x <- c(0.1819711,0.4811463,0.1935151,0.1433675)
> 1-sum(x)
[1] 0

Also check out sum.exact in the caTools package.