Invalid mesh built; different mesh built calling by hand tetmesh

[Marco Morandini]

- running mesh3d.py gives an invalid mesh: at least element number 8 is overlapping elements 3617 and 6147.
- running by hand tetgen with the same options on the saved PLC

tetgen -pzAaq2 pippo

leads to a different number of nodes and elements in pippo.1.ele and pippo.1.node
File naca0012_pan50.dat is required in order to build the mesh.

[Johan Hake (johan-hake)]

Marco!

I see that you get different number of nodes and elements when run from the command line, which is pretty strange in the first place, but how do you analyze that you have overlapping elements?

Maybe you can run with slightly different tetrahedron quality settings?

  plceditor.set_radius_edge_ratio(1.3)?
  plceditor.set_uniform_volume_constraint(somevalue)

I also see that you have not included the hole on the facet with marker 3. When you do that you get another set number of nodes and elements. Why is this out commented?

[Marco Morandini (morandini)]

Apologize for the delayed answer: my university had been closed for almost the whole past week.

> how do you analyze that you have overlapping elements?

I'm attaching the generated mesh; look at tetrahedrons 8, 27948 and 22451. Do you get the same results by running the script?

In the .png, the yellow points are positioned at tetrahedron's 8 node locations.
I've stumblued upon this because dolfin /python) fails to interpolate a solution to a different (refined) mesh. And, if I understand correctly,
this is because the barycenter of tetrahedron 8 falls exactly at the boundaries of tetrahedrons 27948 and 22451. (dolfin/function/Function.cpp, Function::non_matching_eval)

A student that is working on this (he's the one who actually wrote the mesh-generation script)
claims (today) that his mesh is generated correctly; he works on a different system than mine,
so, I suspect some kind of miscompilation. Today I think I've found an issue with tetgen,
and I've written to his author. I don't know, however, if this is reason behind what I'm seeing. The e-mail is copied below.

>Maybe you can run with slightly different tetrahedron quality settings?
>
> plceditor.set_radius_edge_ratio(1.3)?
> plceditor.set_uniform_volume_constraint(somevalue)
>
>I also see that you have not included the hole on the facet with marker 3. When you do that you get another set number of nodes and elements. >Why is this out commented?

I'll look into these.

Thanks,

Marco

----------------------------
Dear Prof. Hang Si

my name is Marco Morandini.

I think I've traced down
(thanks to gcc's -Warry-bounds warning option)
a possible bug. The description below applies to tetgen 1.4.2
(the version distributed by tritetmesh,
https://launchpad.net/tritetmesh ),
but a quick check suggests that, even if line numbers are different, the same problem could still be present in version 1.4.3
(from your download site)

After the loop

    for (newtet.loc = 0; newtet.loc < 4; newtet.loc++) {

(line 22143 of tetgen.cxx)

newtet.loc will be equal to 4;

Then, with

    pointptr = org(newtet);

and

    pointptr = dest(newtet);

(lines 22185 and 22187), you will call the inline methods
triface::org and triface::dest (lines 4460 and 4464) that, in turn,
will access locver2org[t.loc][t.ver], locver2dest[t.loc][t.ver].

Unfortunately locver2org and locver2dest are

    static int locver2org[4][6];
    static int locver2dest[4][6];

Is the above analysis correct?

Thanks for your attention,

Marco Morandini

[Marco Morandini (morandini)]

generated mesh