[Gmsh] Question

Christophe Geuzaine c.geuzaine at ulg.ac.be
Tue Aug 12 23:07:51 CEST 2003

```Josef Novák wrote:
> Hello,
> I have a problem with mesh generating. I have simple *.geo file:
>
> Point(1) = {0, 0, 0, 0.5};
> Point(2) = {1, 0, 0, 0.5};
> Point(3) = {2, 0, 0, 0.5};
> Line (1) = {1, 2};
> Line (2) = {2, 3};
> Extrude Line {1, {0,1,0}};
> Extrude Line {2, {0,1,0}};
> Line Loop(11) = {-3,-4,1,5};
> Plane Surface(12) = {11};
> Line Loop(13) = {7,-9,-2,5};
> Plane Surface(14) = {13};
> Physical Surface(15) = {12,14};
>
> When I use triangle isotropic algorithm, it makes this *.msh file:
>
> \$NOD
> 10
> 1 0 0 0
> 2 1 0 0
> 3 2 0 0
> 4 0 1 0
> 5 1 1 0
> 7 2 1 0
> 8 0.5 0.5 0
> 9 1.5 0.5 0
> 10 0.5 0.5 0
> 11 1.5 0.5 0
> \$ENDNOD
> \$ELM
> 8
> 1 2 15 12 3 2 1 10
> 2 2 15 12 3 10 5 2
> 3 2 15 12 3 4 5 10
> 4 2 15 12 3 1 4 10
> 5 2 15 14 3 3 2 11
> 6 2 15 14 3 11 7 3
> 7 2 15 14 3 5 7 11
> 8 2 15 14 3 2 5 11
> \$ENDELM
>
> It generates multiple points - 8 resp. 10, 9 resp. 11.

Sure: you defined each surface twice (once with 'Extrude Line', once
with 'Plane Surface') -> Gmsh generated two overlapping meshes. Just
remove the Plane Surface commands and everything will be fine:

Point(1) = {0, 0, 0, 0.5};
Point(2) = {1, 0, 0, 0.5};
Point(3) = {2, 0, 0, 0.5};
Line (1) = {1, 2};
Line (2) = {2, 3};
Extrude Line {1, {0,1,0}};
Extrude Line {2, {0,1,0}};
Physical Surface(15) = {6,10};

Christophe

--
Christophe A. Geuzaine
Applied and Computational Mathematics, Caltech
geuzaine at acm.caltech.edu - http://geuz.org

```