[R] R calculates small numbers, where the result should be zero

[Andrea Gonnermann]

Hi all,

my problem is that R does wrong calculations, when the result should be zero.
I have the following code:

 RD_Var1 <- ((0.1*(1-0.1))/100)+((0.2*(1-0.2))/100)
 RD_Var2 <- ((0.1*(1-0.1))/100)+((0.2*(1-0.2))/100)
 RD_1 <- 0.1-0.2
 RD_1
 RD_2 <- 0.1-0.2
 FEM_Eff_RD <- ((1/RD_Var1)*RD_1+(1/RD_Var2)*RD_2)/(1/RD_Var1+1/RD_Var2)
 Q_RD    <- 1/RD_Var1*((RD_1-FEM_Eff_RD)^2)+1/RD_Var2*((RD_2-FEM_Eff_RD)^2)
 Q_RD
My result is:
1.540744e-31
When I put the calculated numbers directly into the last formula, I
get zero, which is the correct answer:
Q_RD    <- 1/0.0025*((-0.1--0.1)^2)+1/0.0025*((-0.1--0.1)^2)

Why does R calculate the other number instead of zero?

Thank you very much for your help!