Examples
========


Geometry and meshing GMSH
--------------------------

We create a very simple geometry: a square with side :math:`1`. Here, we create the points, the lines, the surface; we could also have done it by translation/extrusion...

**NOTE:**

*We create a "physical" that contains the square area of number 107.*


.. code-block:: text

    L=1;

    d=0.45;


    Point (1) = {0, 0, 0, d};

    Dot (2) = {L, 0, 0, d};

    Dot (3) = {L, L, 0, d};

    Dot (4) = {0, L, 0, d};

    Line (1) = {1, 2};

    Line (2) = {2, 3};

    Line (3) = {3, 4};

    Line (4) = {4, 1};

    Line Loop (106) = {2, 3, 4, 1};

    Plane Surface (6) = {106};

    Physical Surface (107) = {6};

The mesh created with the 2D anisotropic algorithm is:


.. image:: images/100000000000018C0000015931B0074ACD8FA6B0.png
    :width: 3.3in
    :height: 2.8752in


.. _RefImage_100000000000018C0000015931B0074ACD8FA6B0.png:

The GMSH mesh file contains the description of the nodes and meshes:


.. code-block:: text

    $ NOD

    9

    1 0 0 0

    2 1 0 0

    3 1 1 0

    4 0 1 0

    5 0.4999999999999931 0 0

    6 1 0.4999999999999931 0

    7 0.500000000000007 1 0

    8 0 0.500000000000007 0

    13 0.5000000000000001 0.5 0

    $ ENDNOD

    $ ELM

    8

    1 2 107 6 3 13 1 5

    2 2 107 6 3 8 1 13

    3 2 107 6 3 5 2 13

    4 2 107 6 3 13 2 6

    5 2 107 6 3 6 3 13

    6 2 107 6 3 3 13 3 7

    7 2 107 6 3 7 4 13

    8 2 107 6 3 13 4 8

    $ ENDELM

The syntax for this file is described in the "File Formats/GMSH mesh file format "section of the GMSH manual.


Aster mesh file produced by operator PRE_GMSH
----------------------------------------------------------


.. code-block:: text

    TITRE

    AUTEUR = INTERFACE_GMSH DATE =17/07/2003

    FINSF

    %

    COOR_3D NBOBJ =9

    % FORMAT =( 1*NOM_DE_NOEUD ,3* COORD)

    N1 0.00000000000000E+00 0.00000000000000E+00 0.00000000000000E+00

    N2 1.00000000000000E+00 0.00000000000000E+00 0.00000000000000E+00

    N3 1.00000000000000E+00 1.00000000000000E+00 0.00000000000000E+00

    N4 0.00000000000000E+00 1.00000000000000E+00 0.00000000000000E+00

    N5 4.99999999999993E-01 0.00000000000000E+00 0.00000000000000E+00

    N6 1.00000000000000E+00 4.99999999999993E-01 0.00000000000000E+00

    N7 5.00000000000007E-01 1.00000000000000E+00 0.00000000000000E+00

    N8 0.00000000000000E+00 5.00000000000007E-01 0.00000000000000E+00

    N13 5.00000000000000E-01 5.00000000000000E-01 0.00000000000000E+00 E+00

    FINSF

    %

    TRIA3 NOM = INDEFINI NBOBJ =8

    M1 N13 N1 N5

    M2 N8 N1 N13

    M3 N5 N2 N13

    M4 N13 N2 N6

    M5 N6 N3 N13

    M6 N13 N3 N7

    M7 N7 N4 N13

    M8 N13 N4 N8

    FINSF

    %

    GROUP_MA NOM = GM107

    M1 M2 M3 M4 M5 M5 M6 M7 M8

    FINSF

    %

    FIN

The eight triangles that make up the mesh square are then accessible in *Aster* in mesh group GM107.