[R] calculate differences - strange outcome

[Bernardo Rangel Tura]

Em Qui, 2008-07-17 às 11:47 +0200, Kunzler, Andreas escreveu:
> Dear List,
> 
> I ran into some trouble by calculating differences. For me it is
> important that differences are either 0 or not.
> 
> So I don't understand the outcome of this calculation
> 
> 865.56-(782.86+0+63.85+18.85+0)
> [1] -1.136868e-13
> 
> I run R version 2.71 on WinXP

Hi Andreas Kunzler,

Your problem is cause by numeric represntation in computer
(Floating-Point numbers) and this topic is explain in R FAQ 7.31

But the solution for your calculations is possible using the "guard
digits" approach, so  if you needd solve:

865.56-(782.86+0+63.85+18.85+0)

Using 

865.56/100 -(782.86+0+63.85+18.85+0)/100

More details in http://docs.sun.com/source/806-3568/ncg_goldberg.html
(This links is indicated in R FAQ 7.31)


-- 
Bernardo Rangel Tura, M.D,MPH,Ph.D
National Institute of Cardiology
Brazil