Correct use of new "interpolate"

[andrewlhicks]

I'm currently trying to convert my code from the old way of interpolating to the new way, i.e. to

from firedrake.__future__ import interpolate

f = assemble(interpolate(some_expr, some_func_space))

While simply doing the old method, i.e.

from firedrake import interpolate

f = interpolate(some_expr, some_func_space)

gives a warning, I noticed that simply writing

f = Function(some_func_space)
f.interpolate(some_expr)

doesn't throw a warning. Is interpolating via the second method (i.e. using the interpolate method as opposed to the freestanding interpolate function) still going to be supported then? I'm asking because I still have lots of code that uses this syntax to interpolate stuff. I'm not sure if I need to rewrite my code in this case.

[connorjward]

The interpolate method of Function (as opposed to the interpolate function) is always evaluated eagerly so you don't need to change anything in that case.

[dham]

The difference is that interpolate the free function now returns a symbol for interpolation, which can be composed with other symbolic operations and evaluated later. That's the change we needed to make to increase composability. Function.interpolate never returned anything and isn't needed as a symbolic operator, so it doesn't change.

[andrewlhicks]

Thanks for your answer. So just to clarify, the two methods of interpolation, i.e.

f = Function(some_func_space)
f.interpolate(some_expr)

and

f = assemble(interpolate(some_expr, some_func_space))

give the same result?

[dham]

Yes, that's correct.