[R] Where precision change

[jim holtman]

FAQ 7.31

?all.equal

On Mon, Oct 18, 2010 at 5:58 AM, Alaios <alaios at yahoo.com> wrote:
> Hello everyone.
> I need some help to understand when number precision in R is set. For this
> please consider the following example
>
>
>  for (i in c(2:length(final))){
>    sizex <- c(sizex,(final[i]-final[i-1],digits=2))) # round is used to remove
> values that are too small like e-17.
>    print(round(final[i]-final[i-1],digits=2))
>  }
>
> final[2]-final[1] return something like 4.440892e-16, which means that these two
> numbers are the same. They are two but as they were derived from a different
> process they are not the same for precision.
>
> Also the line print(round(final[2]-final[1]),digits=2) returns 0 which is
> correct
>
> When the above loop stops executing inside sizex variable I find the value
> 4.440892e-16 which I was not expecting.  As you can see from small code snippet
> before setting the value in the sizex I try to round it. The print gives the
> right value but for some reason it seems that inside the loop the precision in
> sizex is changed.
>
> Can you please help me clarify that?
>
> Best Regards
> Alex
>
>
>
>        [[alternative HTML version deleted]]
>
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-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

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