Transpose interpolation -> adjoint interpolation

[jrmaddison]

Description

Replace transpose interpolation with adjoint interpolation, including the extra complex conjugation.

Fixes #3955

[connorjward]

LGTM

[jrmaddison]

There's the caveat that this

• changes behaviour if using adjoint interpolation via interpolation methods. Transpose interpolation becomes adjoint interpolation.
• changes and corrects behaviour if using interpolation via assembly. Assembly of the adjoint yields the adjoint, as expected.

[connorjward]

There's the caveat that this

• changes behaviour if using adjoint interpolation via interpolation methods. Transpose interpolation becomes adjoint interpolation.
• changes and corrects behaviour if using interpolation via assembly. Assembly of the adjoint yields the adjoint, as expected.

@dham what are your thoughts?

[dham]

There's the caveat that this

• changes behaviour if using adjoint interpolation via interpolation methods. Transpose interpolation becomes adjoint interpolation.
• changes and corrects behaviour if using interpolation via assembly. Assembly of the adjoint yields the adjoint, as expected.

@dham what are your thoughts?

I'm fine with this because I think what James is proposing is mathematically correct. The small number of complex users that will even notice can deal with it.

[connorjward]

@jrmaddison please can you update this branch. We have just merged #3976 which will fix these test failures.

[jrmaddison]

@jrmaddison please can you update this branch. We have just merged #3976 which will fix these test failures.

Done

[jrmaddison]

Updated to use Interpolator directly to work around #3988