Dear Professor Bangerth,
thanks for your reply, I hope I can answer your questions:
I can see that this doesn't look right. But do you understand *why*
> things go wrong? I can't tell from the pictures, but I've often found
> that when trying to solve a problem for which I know that there is a bug
> somewhere, then it's worthwhile investing the time to *understand* why
> it is wrong, rather than trying to come up with completely different
> ways of doing this.
>
Oh yes, I actually did not assume my current way of doing things to work.
After the static case was running, it was just a one liner (calling
set_fe_indices() again in each timestep) which was a really naive way of
doing things.
The problem at the moment is, that I just change the fe_index from pure
FE_Nothing to my actual FE_System without updating my sparsity pattern, and
re-initializing my matrices / vectors.
To be honest I didn't even think, that this code runs in debug mode but
throws an assertion, but it didn't...
So the two option 1 and 2 are the things, that I see, which can "fix" my
problem.
No, I would venture the guess that the cost of assembling and solving
> linear systems is still the dominant factor.
>
That's definitely right. Nevertheless I guess transferring old solutions
with no degrees of freedom on an ancient FE_Nothing cell to an updated
version where this cell has degrees of freedom might become tricky.
The problem with the second way is that just not using FE_Nothing but
instead my normal FE_System and setting all degrees of freedom to "0" on
the former FE_Nothing cells will not help either, since I use continuous
elements and don't want my interior ("0"-solid-solution) to interchange
with my outer (flow)-solution on the "cut-cells". I guess one way to
overcome this issue is to set all DoF on a "former FE_Nothing cell" to "0"
besides the DoFs that also belong to a cut-cell neighbor?
Greetings,
Mathias
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