How do I use a Python function to define Dirichlet boundary conditions which are not known in closed form?

[dokken]

Have a look at UserExpressions, for instance:

Update Expression for DirichletBC

This is because the class of this two objects differs, and is handled differently by the DirichletBC. You can see this with the following code: import ufl print(isinstance(Coeff(T), ufl.Coefficient)) print(isinstance(2*Coeff(T), ufl.Coefficient)) which returns True False This means that the latter input is treated as something that has to be projected internally in the DirichletBC, and is thus not prone to updates. What you should do here is to add a scaling parameter to your UserExpression…

Here, you can substitute self.T with your function, which has to be evaluated at x[0],x[1],x[2]