MixedInterpolator

[pbrubeck]

Description

Enables assembly of the interpolation matrix for mixed spaces

assemble(interpolate(TrialFunction(V1*V2), W1*W2))) -> MatNest([[Interp(v1, w1*), 0], [0, Interp(v2, w2*)]])

We also allow the operand to be any expression, resulting in non-zero off diagonal blocks.

This is the last step required to clean up the special cases of an Interpolate in assemble.py.

[leo-collins]

How will this extend when #3478 goes in and we can define MixedFunctionSpaces on multiple domains?

[pbrubeck]

How will this extend when #3478 goes in and we can define MixedFunctionSpaces on multiple domains?

I believe this approach should give us the matfree adjoint and the forward/adjoint matrices for that case, as long as each MFS component on the source and target are defined on standard, possibly distintict meshes/submeshes.

The base branch was changed.

[pbrubeck]

This needed more work after FEniCS/ufl#422 was merged. We now split the sub interpolators via the same mechanism that handles fieldsplit, so this should be much cleaner.

[connorjward]

I think I'm mostly happy now. Definitely good to see so much deleted code.

There could definitely be more docstrings and type hints but there are at least some.