Reactive terms that depend on the value of the field variables and other condition

[dokken]

You can use a conditional, see:

https://fenics.readthedocs.io/projects/ufl/en/latest/manual/form_language.html?highlight=Conditional%20#conditional

and

Using Conditional function inside a Project function

The problem is that you try to assign a function (the result of the projection), to a float. The initial kappa has to be a function. This is illustrated in the minimal example below. Please note the following: Your proposed example is not minimal, and contains alot of variables not required to reproduce the error. The example below should be used as a guideline for further inquires. To represent kappa, I am using a DG space, as kappa is discontinuous. If you decide to use a CG space, you wil…