[firedrake] absolute value of gradient

[George Ovchinnikov]

Hello folks,

I have a scalar field in 2D, $w$, say:

V = FunctionSpace(mesh, "CG", 1)
w  = Function(V)
w.interpolate(Expression("1"))

and I need too find an norm of grad(w) in every point of the given area,
i.e. get a scalar field back.

I've found no way to iterate through individual elements of grad(w) to
be able to do in manually, neither abs(grad(w)) or something similar
works. Any ideas? Do I need to solve some variational problem for this,
too?

Sincerely,
George