Dear R people
I came across a strange thing:
sd(rep(0.01, 15)) #0 sd(rep(0.001, 15)) #4.489023e-19 sd(rep(0.00001, 15)) #0 sd(rep(0.00000001,15)) #1.712427e-24
sd(rep(0.01, 13)) #1.805557e-18 sd(rep(0.001, 13)) #4.513894e-19 sd(rep(0.00001, 13)) #0 sd(rep(0.00000001,13)) #0
sd(rep(5.01, 15)) #0 sd(rep(5.001, 15)) #4.489023e-19 sd(rep(5.00001, 15)) #1.838704e-15 sd(rep(5.00000001,15)) #9.19352e-16
sd(rep(5.01, 13)) #9.244454e-16 sd(rep(5.001, 13)) #9.244454e-16 sd(rep(5.00001, 13)) #1.848891e-15 sd(rep(5.00000001,13)) #0
Why gives sd sometimes zero and sometimes values close to zero and why does it depend on the value and on how many times it is repeated? Shouldn't it give always zero? Is there a way to control this?
I use R Version 1.8.1 under UNIX.
Thanks for any suggestions!!
Andreas
I think this is due to expected inaccuracy of numerical floating point representation (and also happens for me under WinNT 4.0, R-1.9.0 beta).
And for the largest value you have listed all.equal(1.848891e-15, 0) is still TRUE.
Uwe Ligges
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