Topics: Numerical Analysis
The absolute error is the distance between the exact value and the approximate value. It’s given by:
Compare the relative error.
If the Exact Value isn't Known
If the exact value isn’t known (i.e. we’re using a numerical method to find it), then is the last approximation we got, and the penultimate one.
This can only be done with convergent numerical methods, since this ensures our last approximation is better than the one before.