[Gmsh] 2D: physical volume tags

[Nico Schlömer]

Okay, figured it out: For 2D, you don't want "Physical Volume" but
"Physical Surface".


On Fri, Nov 2, 2012 at 3:51 PM, Nico Schlömer <nico.schloemer at gmail.com>wrote:

> Hi all,
>
> I'm trying to define a 2D mesh with regions. To this end
>
> =================== *snip* ===================
> Function Rectangle
>   // Points.
>   cp1 = newp;
>   Point(cp1) = {xmin,ymin,z,lcar};
>   cp2 = newp;
>   Point(cp2) = {xmax,ymin,z,lcar};
>   cp3 = newp;
>   Point(cp3) = {xmax,ymax,z,lcar};
>   cp4 = newp;
>   Point(cp4) = {xmin,ymax,z,lcar};
>
>   // Lines.
>   cl1 = newreg;
>   Line(cl1) = {cp1,cp2};
>   cl2 = newreg;
>   Line(cl2) = {cp2,cp3};
>   cl3 = newreg;
>   Line(cl3) = {cp3,cp4};
>   cl4 = newreg;
>   Line(cl4) = {cp4,cp1};
>
>   loop = newreg;
>   Line Loop(loop) = {cl1,cl2,cl3,cl4};
>   surf = newreg;
>   Plane Surface(surf) = {loop};
>
>   Physical Volume(Sprintf("rectangle %g", t)) = surf;
>
> Return
>
> // Build two rectangles.
> lcar = 0.1;
> z = 0;
> ymin = -1.0;
> ymax= 1.0;
>
> t = 0;
> xmin = -1.0;
> xmax = 0.0;
> Call Rectangle;
>
> t = 1;
> xmin = 0.0;
> xmax = 1.0;
> Call Rectangle;
>
> Coherence;
> =================== *snap* ===================
>
> Meshing this works well, and when saving the data as MSH-file, I get
>
> =================== *snip* ===================
> $MeshFormat
> 2.2 0 8
> $EndMeshFormat
> $PhysicalNames
> 2
> 3 1 "rectangle 0"
> 3 2 "rectangle 1"
> $EndPhysicalNames
> $Nodes
> 504
> 1 -1 -1 0
> 2 0 -1 0
> 3 0 1 0
> [...]
> $EndNodes
> $Elements
> 1031
> 1 15 2 0 1 1
> [...]
> 1023 2 2 0 12 344 455 494
> 1024 2 2 0 12 355 476 464
> 1025 2 2 0 12 344 441 501
> 1026 2 2 0 12 344 494 441
> [...]
> =================== *snap* ===================
>
> I'm wondering about the tags for the elements here. It seems that the tags
> are "0" and "12", one of which I would expect to correspond with a
> PhysicalName.
> Can anyone enlighten me about the meaning of the tags here and how they
> correspond with physical volumes?
>
> Cheers,
> Nico
>
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