[dune-pdelab] SOLVED: Output component gradients for PowerGridfunctionSpace

[Michael Wenske]

Dear all,

i managed to do the gradient outputs for the components of the PowerGFS
by writing an aditional discrete Gridfunction which is compatible with
the adapters.
I am not sure if it is clean enough to make it into the gfs utilities
header, but
for closure I want to report it here. (see attached header)

Michael

On 14.11.19 15:36, Michael Wenske wrote:
> Dear wizards,
>
> i am working on a system of one or two (or more) reaction-diffusion
> equations. I successfully
> refactored my codebase to use the PowerGridfunctionSpace for this
> application.
> This way I can extend my system to more fields, or fall back to the
> simple one-equation case.
> I can switch between a PowerGFS of size 1 (one equation), and size 2
> (two coupled equations),
> and export the results to VTK. So far so good.
>
> Now I want to inspect the gradients of my field(s). In the normal case
> without the PowerGFS,
> I could make use of the functionality of DiscreteGridFunctionGradient,
> and then use the VTK adapter to write the gradient. This is very convenient!
>
> How do I go about this when using a PowerGFS? I fail to get it to work
> even for the
> one-component PowerGFS. For the two component fields I can use the class
> VectorDiscreteGridFunction<..,size>, and force the return types size
> with the last
> template argument. The class VectorDiscreteGridFunctionGradient does not
> seem
> to have that option. Here, in the case where the powerGFS has size one, the
> Adapters can not convert the one-component Fieldvector to double (I think).
>
> I tried a different route of extracting the sub-GFS-Type from the
> PowerGFS and
> create a handle on the first components subspace. The idea was to use
> use the existing
> functionality of the DGF's and adapters on the subGFS, but I also run
> into problems.
> How would I extract the (smaller) coefficient vector from the larger
> PowerGFs one?
>
> I figure that this might be interesting for other applications too,
> where the GFS-Tree
> might be even more complex than in my case.
>
> I am attaching a minimal working example (dune module) which outputs the
> two component fields
> sucessfully. The parts where I horribly fail to output the gradients of
> the first component are
> commented, starting from line 107. I would appreciate any hints or
> insights on how to do this.
>
> Am I missing something? What would be the dune way to do this?
>
> build with:
> ./dune-common/bin/dunecontrol --opts=./dune-powerGFS-output/debug_opts
> --only=dune-powerGFS-output all
>
> I am working on dune 2.6
>
> thanks in advance!
>
> Michael
>
>
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