Issues with transfer operators

[brownbaerchen]

I started looking into the transfer operators a little bit and noticed some issues. I will collect what I find here because I don't know if I have time to fix everything.

Side effects of MultiComponentMesh

First of all, there are some side effects of the implementation of imex_mesh via MultiComponentMesh. I have seen, for instance here:

if isinstance(G, mesh):
    ...
elif  isinstance(G, imex_mesh):
    ...

However, because an object is an instance of all classes its own class is derived from, an imex_mesh object is also an instance of mesh and the wrong condition will be entered. I expect we need to be mindful of this distinction throughout the code, not just in the transfer classes. I suggest instead:

if type(G).__name__ == "mesh":
    ...
elif type(G).__name__ == "imex_mesh":
    ...

The type function contains no information about inheritance and by using __name__, we can check against a string and avoid importing the data type. This will be handy for GPU agnostic code. Eventually, I want if type(G).__name__ in ["mesh", "cupy_mesh"]:.

Want non-normalised grids

I tested the order of interpolation and restriction for some classes. Here are some limitations I found:

• [ ] mesh_to_mesh interpolation and restriction work only for grids normalised to 1

Feel free to check the boxes after a respective fix. Let me know when you find more restrictions or add them to this issue yourself.

[pancetta]

Huh, interesting.. you're right, the transfer operations are not as generic as I thought. For mesh_to_mesh I understand this, but are your sure about mesh_to_mesh_fft?

[pancetta]

👍 for the first item.

[brownbaerchen]

Huh, interesting.. you're right, the transfer operations are not as generic as I thought. For mesh_to_mesh I understand this, but are your sure about mesh_to_mesh_fft?

No, I think mesh_to_mesh_fft is fine actually. I got stuff mixed up ;)