IDEA: Proxy block for adjoint about firedrake

[dham]

I think this is something like where we ought to go. I'm not sure whether proxy block is the right way to do it.

The way we share state between forward solves right now is by having all the related solve blocks share some state information. This could be expanded to more shared state (particularly the adjoint solves).

I think it would be worth fleshing out which of these approaches is preferable. Maybe put it on the meeting agenda.

[colinjcotter]

I like this idea of leaving it up to the coder to decide

[dham]

I like this idea of leaving it up to the coder to decide

I don't think either of these options does that. This is still the same taping process.

What is proposed is that if a e.g. NonLinearVariationalSolver has its solve method called twice, you either get:

1. A Solve block the first time and then a Proxy block pointing at the Solve block the second time.
2. Two solve blocks but they both have an (e.g.) ._ad_block_shared_state member which contains the data that is shared between the two blocks (the forward and adjoint solvers, for example).

[connorjward]

A related pipe dream of mine is for us to employ enough smart caching that we could get near to equivalent performance calling the solve function compared with creating and reusing solvers.

This would all be interesting to discuss in this week's meeting.