Prerequisites

Once installed, mmg can be used as a command-line tool in any given shell. Three different software are produced by the compilation, one for each given configuration: mmg2d, mmgs, mmg3d.

A help message containing a summary of the main options may be printed:

mmg3d_O3 -h

Input data

Mesh data

Input meshes may be provided in several different formats:

  • .mesh/.meshb : ASCII/binary Medit file formats

  • .msh/.mshb : ASCII/binary gmsh file formats

  • .vtk/.vtp/.vtu : Paraview file formats

Input meshes must be conformal. An input mesh name, which may be specified without the extension, is mandatory and is the only positional argument of mmg.

Using gmsh, it is possible to convert many different file formats to medit file format .mesh:

Save As -> Mesh - INRIA Medit (*.mesh)

For two-dimensional meshes, there is a non-compatibility between the .mesh format used by mmg2d (with coordinates in 2D) and gmsh output (with coordinates in 3D).

  • To force mmg2d to produce a .mesh file readable by gmsh, run mmg2d with the -3dMedit 1 command line argument.

  • To load a 2D .mesh file created with gmsh, run mmg2d with the -3dMedit 2 command line argument. In this case, the .mesh file produced by mmg2d is a gmsh .mesh.

  • To load a 2D .mesh file created with gmsh and save it as a Medit 2D .mesh file, run mmg2d with the –3dMedit 3 command line argument.

Paraview file formats require access to the VTK library. It must be linked to mmg when compiling. In .vtk file formats, domain references (resp. node references) can be provided using cell data (resp. point data) with the medit:ref array name.

Metric data

For mesh adaptation with respect to a given metric (or size map), metric data should be provided according to mesh file format.

Medit file format

  • metric data may be provided as a Medit solution file (.sol extension). If the file has the same name as the mesh file, it is automatically opened and treated as metric data (assuming that level-set discretization mode is disabled).

  • -met/-sol options may be indistinctly used to specify the file name if it different from the mesh file name.

  • In level-set discretization mode, metric files are ignored by default and must be loaded with the -met option.

GMSH file format (.msh or .mshb): size map data should be provided in the mesh file as \$NodeData and flagged using a string tag with the :metric suffix.

VTK file formats (.vtk or .vtu): a point data field should be given in the mesh file with the name :metric.

Solution file for level-set discretization

For level-set discretization mode (-ls option), solution data should be provided. Similarly to metric data, its format depends on mesh file format.

Medit file format

  • solution data may be provided as a Medit solution file (.sol extension). If the file has the same name as the mesh file, it is automatically opened and treated as solution data.

  • -sol options may be used to specify the file name if it different from the mesh file name.

GMSH file format (.msh or .mshb): level-set must be provided in the .msh(b) file as $NodeData

VTK file formats (.vtk or .vtu): level-set must be provided in the mesh file as point data with the :ls suffix.

Lagrangian displacement

To perform the lagrangian motion of an object, it is necessary to provide:

Medit file format: a displacement at Medit solution file format (.sol extension).

GMSH file format (.msh or .mshb): displacement data must be provided in the .msh(b) file as $NodeData.

VTK file formats (.vtk or .vtu): displacement data must be provided in the mesh file as point data.

Output data

By default, the output mesh file format is identical to the input mesh file. Its name is identical, with the string .o added between the mesh name and its extension. For example, if the input mesh is called my-mesh.mesh, the output file will be called my-mesh.o.mesh. To provide an output file name and to enforce a specific file format, option -out may be used.

Alongside the output mesh file, a output solution file is produced as well. This file contains the targeted metric during adaptation over the output mesh. The default naming convention is identical to the one for meshes. In our example, the output solution file would be called my-mesh.o.sol. It is not possible to provide a custom name for this file.

Mesh visualization

  • Medit: for visualizing meshes at Medit file formats.

  • gmsh: for visualizing meshes at Medit file formats without associated solution file or gmsh files with embedded solution data.

  • Paraview: for visualizing meshes at VTK file formats.