I didn’t mean to sound too harsh, sorry for that. I could spot the mistake
right away because it is a mistake I do all the time.
No embarrassment is needed, and no question is ever a stupid question. Don’t
worry! I’ve been in your shoes so many times I cannot count them anymore…
:)
Luca.
> On 11 Jan 2023, at 14:33, Abbas <abbas.ballou...@gmail.com> wrote:
>
> Well, this is embarrassing.
> Thank you very much
>
> On Wednesday, January 11, 2023 at 3:11:11 PM UTC+2 luca....@gmail.com wrote:
> You have an issue in your boundary worker.
>
>
> The boundary worker is called passing a cell, a face_no, scratch, and copy.
> Yet, in your code, you loop again on the faces of the cell:
>
>
> for (const auto &face : cell->face_iterators())
> {
> if ( ((face->boundary_id() == 0) || (face->boundary_id() == 1)))
>
>
> this should become
>
> if((cell->face(face_no)->boundary_id() == 0) ||
> (cell->face(face_no)->boundary_id() == 1) {
>
> …
>
> }
>
> otherwise, you are going to assemble the face terms twice on the four
> corners.
>
> Best,
> Luca.
>
> > On 11 Jan 2023, at 12:05, Abbas <abbas.b...@gmail.com> wrote:
> >
> > Hello,
> >
> > Setting:
> > 1) Unit square domain,
> > 2) Simple scalar Laplacian with no source term.
> > 3) 0 and 1 Dirichlet on opposite ends of the square and zero Neumann on the
> > other two edges.
> >
> > I am trying to solve the above problem using SIPG by adopting step 74. The
> > expected solution should be perfectly linear with a constant gradient as
> > the problem reduces to a pseudo 1-D problem.
> >
> > That is the case if I use CG, but with DG I do not get a perfectly linear
> > solution and that is causing me problems.
> >
> > I have attached below a single image file that includes:
> > 1) The solution.
> > 2) The solution gradient with weird behaviour at the corners
> > 3) Line plot of the solution across the lower wall.
> >
> > and the code I am using which is based on step 74.
> >
> > Things I tried/looked into:
> > - I tried to adapt the code to CG and I get the expected results. I can't
> > straight up impose BCs strongly with DG here.
> > - I am sure this isn't a Paraview issue because I tried integrating across
> > the boundary within deal and I am getting mesh dependent results.
> > - The weak form is correct. The Neuman BC shows up as a boundary integral
> > in the rhs which has no contribution. (Neumann zero at these walls).
> > - I looked into the distributed LDG method within the dealii gallary and
> > adopted it to these BCs and I didn't have this problem.
> >
> > The only thing I haven't tried yet is to do a simple problem by hand and
> > compare the dealii and my outputs. Before doing that, any ideas on how I
> > can debug this? Is this something associated with imposing BCs weakly with
> > SIPG and will happen no matter what?
> >
> > best,
> > Abbas
> >
> >
> >
> > --
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> >
> > <Screenshot from 2023-01-11 12-39-11.png><SIPG.cc>
>
>
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