I want to change this by a python source to add a feature to my model.
Question: How does the Python source term relate to the other three options “Nodal”, “Line”, “Volumetric”? Is the Flux integrated later in OGS or directly used for the residual? The second one would be the option I’d like to have.
the Python source term is similar to the Volumetric source term: it will be integrated over the mesh elements. I.e., the integrand will be evaluated at the integration points of the mesh elements.
In fact, the volumetric and the line source term share the same implementation. The term Line only underlines that the integration will be over a line, not a 3D element. But there are no checks AFAIK, you can use either of them for all dimensions (but please be not confused by that)