The Approximation error (benaderingsfout) is the difference between a calculated value and the real value. By dividing it by the real value you get the relative error. A bit relative error indicates bad calculation.
The largest relative error between two arrays as percentage:
np.mean(abs(calculated - real)) # Average of the absolute errors np.mean(abs(calculated - real) / real ) # Average of the differences relative to the real values np.mean(abs(calculated - real) / real ) * 100 # The relative error as percentage.