Unable to add relative errors with reference model

[cverstege]

❓ Question received via feedback:
I want to add a relative model error, but this doesn't work!
I'm running the following code:

>>> from kafe2 import XYContainer, Fit
>>> data = XYContainer([1,2,3], [1,7,19])
>>> data.add_error(axis="y", err_val=0.1, relative=True, reference="model")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: XYContainer.add_error() got an unexpected keyword argument 'reference'

[cverstege]

This behaviour is expected 💡:
The data itself doesn't know the model yet. All uncertainties added to the data container will be uncertainties on the data only.
If you want to set an uncertainty with a reference to the model, use the add_error function of the Fit object instead. The fit has knowledge about both, the data 📊 and the model 📈.

>>> from kafe2 import XYContainer, Fit
>>> data = XYContainer([1,2,3], [1,7,19])
>>> fit = Fit(data)  # this defaults to a line fit, with the model y=a*x+b
>>> fit.add_error(axis="y", err_val=0.1, relative=True, reference="model")

If you want to add a relative error to the data, use reference="data" instead.