FREEFEM_MSH_IO
Read and Write FreeFem MSH files

FREEFEM_MSH_IO, a MATLAB library which can read and write files used by the FreeFem finite element program to store mesh information.

Note that the GMSH program creates mesh files that use the ".msh" extension, but which are an entirely different format.

The msh file format is obliquely described in section 12.5 of the FreeFem documentation.

At least for the 2D case of a triangular mesh, the format seems to be as follows:

a single line giving NV, NE, NT, the number of vertices, boundary edges, and triangles
NV lines, each containing the (X,Y) coordinates and integer label for a node.
NT lines, each containing three vertex indices and integer label for a triangle.
NE lines, each containing two vertex indices and integer label for a boundary edge.

The "labels" seem to be "0" for interior objects and 1 for boundary objects. All edges are boundary objects. (This might not be true. A geometry might include internal edges, and perhaps these count as interior objects, but definitely, the edge list does not include arbitrary triangle edges, only those on the boundary.) All triangles are interior objects. Vertices may be boundary or interior objects.

Licensing:

The computer code and data files made available on this web page are distributed under the GNU LGPL license.

Languages:

FREEFEM_MSH_IO is available in a C version and a C version and a FORTRAN90 version and a MATLAB version and a Python version.

Related Data and Programs:

BAMG, examples which illustrate the use of BAMG, a program for generating 2D meshes that can be used to define the geometry for the the finite element package FREEFEM.

FREEFEM++, examples which illustrate the use of the FREEFEM++ package, a high-level integrated development environment for the numerical solution of nonlinear multiphysics partial differential equations (PDE's) in 2D and 3D.

FREEFEM++_MSH, a data directory which contains examples of the mesh files created by the FreeFem++ program, which use the extension ".msh".

freefem_msh_io_test

MITCHELL_FREEFEM++, examples which illustrate the implementation of the Mitchell 2D elliptic partial differential equation (PDE) test problems using FREEFEM++.

Reference:

Frederic Hecht,
New development in FreeFem++,
Journal of Numerical Mathematics,
Volume 20, Number 3-4, 2012, pages 251-265.
Frederic Hecht,
BAMG: Bidimensional Anisotropic Mesh Generator,
draft version v1.00, December 2006.

Source Code:

freefem_msh_io_2d_data_example.m, sets data for a 2D example.
freefem_msh_io_2d_data_print.m, prints data.
freefem_msh_io_2d_data_read.m, reads data from an FFMSH file.
freefem_msh_io_2d_size_example.m, sets sizes for a 2D example.
freefem_msh_io_2d_size_print.m, prints sizes.
freefem_msh_io_2d_sizes_read.m, reads sizes from an FFMSH file.
freefem_msh_io_2d_write.m, writes sizes and data to an FFMSH file.
i4mat_transpose_print.m, prints an I4MAT, transposed.
i4mat_transpose_print_some.m, prints some of the transpose of an I4MAT.
i4vec_print.m, prints an I4VEC.
mesh_base_one.m adjusts a mesh to use 1-based indexing.
r8mat_transpose_print.m, prints an R8MAT, transposed.
r8mat_transpose_print_some.m, prints some of an R8MAT, transposed.
timestamp.m, prints the current YMDHMS date as a time stamp.