R の .Machine$double.eps
the smallest positive floating-point number x such that 1 + x != 1. It equals double.base ^ ulp.digits if either double.base is 2 or double.rounding is 0; otherwise, it is (double.base ^ double.ulp.digits) / 2. Normally 2.220446e-16.
> options(digits=16)
> .Machine$double.eps
[1] 2.220446049250313e-16
> 2^-52
[1] 2.220446049250313e-16
Python では，
>>> import sys
>>> sys.float_info.epsilon
2.220446049250313e-16
... 同じだ
追記 2021/05/19
Julia だと，
julia> eps()
2.220446049250313e-16
julia> 2^-52
2.220446049250313e-16
