[R] sensitivity logical operators in R

Marc Jekel feuerwald at gmx.de
Mon Jan 24 20:48:27 CET 2011

Hi again,

I have checked the same code (see below) using MATLAB. It produces the 
same error (i.e., equal numbers are evaluated as unequal). Do I miss 

Thanks for help!


Marc Jekel schrieb:
> Hello R Fans,
> Another question for the community that really frightened me today. 
> The following logical comparison produces a "false" as output:
> t = sum((c(.7,.69,.68,.67,.66)-.5)*c(1,1,-1,-1,1))
> tt = sum((c(.7,.69,.68,.67,.66)-.5)*c(1,-1,1,1,-1))
> t == tt
> This is really strange behavior. Most likely this has something to do 
> how R represents numbers internally and the possible sensitivity of a 
> computer? Does anyone know when this strange behavior occurs and how 
> to fix it?
> Thank you all! This list is pleasure!!!
> Marc

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