From the python uncertainties package:
Correlations between expressions are correctly taken into account. Thus, x-x is exactly zero, for instance (most implementations found on the web yield a non-zero uncertainty for x-x, which is incorrect).
x is a single value, with an uncertainty. What does correlation mean in this context?
Example code to illustrate what it's talking about:
In : from uncertainties import ufloat, umath In : x = ufloat(2,1) In : x Out: 2.0+/-1.0 In : y = ufloat(2,1) In : y Out: 2.0+/-1.0 In : z = umath.log(umath.exp(x)) In : z Out: 2.0+/-1.0 In : x-y Out: 0.0+/-1.4142135623730951 In : x-z Out: 0.0+/-0
In this example,
z are all single values with an uncertainty. I don't understand how two single values can be "correlated".
In a practical sense, I'd also be interested to know how
uncertainties actually keeps track of this "correlation".
Further, why doesn't this include some of the uncorrelated error between x and z?
In : b=x+y In : c=y+z In : b-c Out: 0.0+/-0