Bartosz Sawicki wrote:
>>> For example, I think about grad/rot/div operators. In the simpliest case
>>> /demo/pde/poisson, discrete function u is computed. Having u, I would
>>> like to compute also e=-grad(u). Of course, I can write own code
>>> iterating over cells and calculate gradient, but it won't be very
>>> elegant solution.
>>> How would you solve such problem?
>> Define a form that projects whatever quantity you need to a suitable
>> space. Say you want to compute the gradient of a piecewise linear function:
>>
>> P1 = FiniteElement("Lagrange", ..., 1)
>> P0 = VectorElement("Lagrange", ..., 0)
>
> Thank you. Here we can feel power and flexibility of form compiler :)
>
> For archiving correctness I have to add, that my experiments (and also
> your FCC manual) shows that it can't be VectorElement("Lagrange",
> "tetrahedron", 0). Minimal degree for Lagrange elements is 1, only
> discontinuous Lagrange allows zero degree.
> So it should be:
> P0 = VectorElement("Discontinuous Lagrange", "tetrahedron", 0)
>
>> Note that you can also define functionals like the integral of u along
>> the boundary, the average etc. (Use M instead of a, L in FFC.)
>
> Yes, I've noticed demo/pde/functional example. This feature can be very
> useful, but I can't found anything about it in FCC User Manual. It is
> newer that documentation?
It seems to be missing. I've put it on the TODO list (for FFC).
/Anders
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