r - Precision: (1-1e-17)==1 -


what's precision of r? can change it? find (1-1e-16)==1 false, (1-1e-17)==1 true.

i tried calculate

x = 1e-17 q1 = qnorm(x) q2 = qnorm(1-x)

theoretically q1==-q2, output of r 

>  x=1e-17 >  qnorm(x) [1] -8.493793 >  qnorm(1-x) [1] inf

any way avoid such difference?

floating point precision depends on system. can relevant information help(".machine").

e.g., double.eps "the smallest positive floating-point number x such 1 + x != 1".

.machine$double.eps #[1] 2.220446e-16

and double.neg.eps "a small positive floating-point number x such 1 - x != 1".

.machine$double.neg.eps #[1] 1.110223e-16

-

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