[Gmsh] nodes are generated but not used in the tetra mesh

Christophe Geuzaine cgeuzaine at ulg.ac.be
Mon Mar 22 11:54:51 CET 2010

```On 22/03/10 11:22, Umut Tabak wrote:
> Dear developers,
>
> A colleague, Alexander from Delft University of Technology, in the CC
> list of the mail, came up with sth strange for tetra mesh generation for
> a cylindrical geometry. In the attach, you can find the geometry and we
> can mesh the structure using
>
> gmsh cylinder.geo -3
>
> But there is a problem in the generated mesh structure, nodes 1 and 7
> are not used in the element connectivities, where the allocation of the
> system matrices are done with reference to node count and the number of
> degrees of freedom. This results in a gap in the element matrices where
> problems start to pop up in the eigenvalue computations. The geometry is
> attached.
>
> We would appreciate comments on this topic.
>

Hi Umut - If you don't define physical groups Gmsh saves all the
elements in the output mesh file (i.e., also "point" elements associated
with all the points in the geometry).

To save only the elements (and associated vertices) that you want, just
define a physical group. For example in your case:

//
lc = 0.05;
//
Point(1) = {0, 0, 0, lc};
Point(2) = {0.1, 0, 0, lc};
Point(3) = {0, 0.1, 0, lc};
Point(4) = {-0.1, 0, 0, lc};
Point(5) = {0, -0.1, 0, lc};
//
Circle(6) = {2, 1, 3};
Circle(7) = {3, 1, 4};
Circle(8) = {4, 1, 5};
Circle(9) = {5, 1, 2};
//
Line Loop(10) = {6,7,8,9};
Plane Surface(11) = {10};
//
Extrude {0,0,1.5} {
Surface{11};
}

Physical Volume("my volume") = 1;

> Best,
> Umut
>
>
>
> _______________________________________________
> gmsh mailing list
> gmsh at geuz.org
> http://www.geuz.org/mailman/listinfo/gmsh

--
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science
http://www.montefiore.ulg.ac.be/~geuzaine

```