[R] rounding in calculation

[Gabor Csardi]

Read R FAQ 7.31 ?

http://cran.r-project.org/doc/FAQ/R-FAQ.html#Why-doesn_0027t-R-think-these-numbers-are-equal_003f

Gabor

On Fri, Mar 21, 2008 at 04:17:28PM +0100, John Lande wrote:
> dear all,
> 
> I report a problem very simple, that I does non know how to handle.
> 
> look at the following code:
> 
> > a = rep(16.256, 5)
> > sum(a[1:5]^2) - (sum(a[1:5])^2/5)
> [1] 2.273737e-13
> 
> as you can see i retrieve a non 0 value, when i am expected to. what can I
> do?
> 
> > sessionInfo()
> R version 2.6.2 (2008-02-08)
> i386-pc-mingw32
> 
> locale:
> LC_COLLATE=Italian_Italy.1252;LC_CTYPE=Italian_Italy.1252;LC_MONETARY=Italian_Italy.1252;LC_NUMERIC=C;LC_TIME=Italian_Italy.1252
> 
> attached base packages:
> [1] stats     graphics  grDevices utils     datasets  methods   base
> 
> loaded via a namespace (and not attached):
> [1] rcompgen_0.1-17
> 
> 	[[alternative HTML version deleted]]
> 
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-- 
Csardi Gabor <csardi at rmki.kfki.hu>    UNIL DGM