Trying to add new variable in sei_growth.py

[loveinSH]

Hello, I am trying to add a new variable to tune the value of j_sei.
So I added it like this in submodel part sei_growth.py

def get_coupled_variables(self, variables):
    phase_param = self.phase_param
    # delta_phi = phi_s - phi_e
    T = variables["Negative electrode temperature"]
    j_sei_test = variables["j_sei_test"]

Meanwhile I have defined j_sei_test in lithium-ion-parameters like this.
self.j_sei_test = pybamm.Variable('j_sei_test')

But once I added j_sei_test, it will raise a error:
pybamm.expression_tree.exceptions.ModelError: Missing variable for submodel 'negative primary active material': 'X-averaged SEI interfacial current density'.
Check the selected submodels provide all of the required variables.

I am not sure what is the problem now.

[valentinsulzer]

when you create a Variable it needs to be added to model.rhs or model.algebraic, and also to model.initial_conditions.
If you just want j_sei_test to be a fixed value you should make it a Parameter.