Code_Aster native mesh (.mail)

The .mail file is Code_Aster's own ASCII mesh, the one LIRE_MAILLAGE(FORMAT='ASTER') reads and that Salome-Meca and Code_Aster's PRE_GMSH/PRE_IDEAS converters write. It is a sequence of blocks, each opened by a keyword and closed by FINSF, and the file ends at FIN. Nodes and elements are identified by name (N1, M1, NO123…), not by number, and groups refer to those names.

Format name	code_aster
Extensions	.mail (also recognised by content: a leading TITRE or COOR_nD)
Read / Write	✓ / ✓
Extra dependencies	—

Reading & writing

import meshioplusplus

mesh = meshioplusplus.read("model.mail")        # points, cells, GROUP_MA/GROUP_NO as regions
meshioplusplus.write("out.mail", mesh)          # or meshioplusplus.code_aster.write(...)
meshioplusplus.write("out.med", mesh)           # the same mesh as MED, for Salome

Neither read nor write takes extra options. Both engines (the C++ core and the pure-Python reference) read the same meshes and write the same bytes.

Syntax

The reader follows Code_Aster's own reader (lrmast.F90 and the routines it calls) rather than a looser reading of the manual:

• Tokens are separated by blanks or commas. % starts a comment that runs to the end of the line. Keywords are case-insensitive, and names are case-sensitive.
• Only the first 80 columns of a line are read, as in Code_Aster (lirlig.F90 reads A80). A line with content past column 80 gets one warning, and that content is ignored.
• A record is a token stream. An element's node names, or a node's coordinates, may continue on the next lines. Code_Aster's own writer puts an element name and 8 nodes on a line, then 8 per continuation line.
• Block-header options (NOM=, NBOBJ=, NUMIN=, AUTEUR=, DATE=, …) may follow the keyword on the same line or on the next ones. KEY = VALUE with spaces is read as KEY=VALUE. Only NOM= is used, as a group's name.
• Coordinates are Fortran reals or integers (1, 1., .5, 1.E+0, 10.D-1). inf, nan and other spellings are errors.

Keyword	Maps to
COOR_1D / COOR_2D / COOR_3D	the points, with a point dimension of 1, 2 or 3
POI1	vertex
SEG2 / SEG3 / SEG4	line / line3 / line4
TRIA3 / TRIA6 / TRIA7	triangle / triangle6 / triangle7
QUAD4 / QUAD8 / QUAD9	quad / quad8 / quad9
TETRA4 / TETRA10	tetra / tetra10
PENTA6 / PENTA15 / PENTA18	wedge / wedge15 / wedge18
PYRAM5 / PYRAM13	pyramid / pyramid13
HEXA8 / HEXA20 / HEXA27	hexahedron / hexahedron20 / hexahedron27
GROUP_MA	a cell region; dim is the highest dimension of its elements
GROUP_NO	a point region
TITRE, DUMP, DEBUG, GROUP_FA, SYS_UNIT, SYS_COOR, MACRO_AR, MACRO_FA, MACRO_EL, MATERIAU	skipped silently, as Code_Aster does
anything else (SEG22, TR3QU4, a typo)	skipped with one warning per keyword

Each element block becomes one cell block, in file order. A group's name is its NOM= value, or else the block's first token. Groups have no number, so regions carry no tag. A name used for both a GROUP_MA and a GROUP_NO gives two regions. Two blocks with the same name and kind are merged, with a warning.

Node order

The .mail node order is not MED's, although the two formats come from the same code. Code_Aster's MED reader (lrmtyp.F90) permutes every 3-D element between the two. meshio++ keeps the .mail order in the "code_aster" tables of the node-ordering registry:

• The linear cells, TETRA10 and PYRAM13 use meshio++'s (VTK's) order unchanged.
• HEXA20/HEXA27 and PENTA15/PENTA18 list the mid-edge nodes of the bottom ring, then the vertical mid-edges, then the top ring (VTK puts the verticals last), then HEXA27's face centres (1234, 1265, 2376, 3487, 1485, 5678) and body centre, or PENTA18's quadrilateral face centres.

The tables come from Code_Aster's gmsh reader (inigms.F90) composed with meshio++'s gmsh tables. They were also run over the 565 .mail meshes of Code_Aster's own test suite (read locally, not redistributed). Both engines read every one identically, and more than 97% of the quadratic edges have their mid-node within 5% of the edge midpoint (the rest are genuinely curved or collapsed edges). The tables are also checked against Code_Aster's MED reader: both routes give the same element, up to a symmetry of the reference cell. The test fixtures are written in Code_Aster's numbering from the edge lists above. The tests check that every mid-edge node lands on its meshio++ edge midpoint and that every solid is positively oriented.

Writing

• A % provenance block, then one COOR_nD block (n = the point dimension), one element block per cell block, a GROUP_NO per point region and a GROUP_MA per cell region, then FIN.
• Nodes are named N1… and elements M1…, numbered in block order. Names are limited to 8 characters, so more than 9,999,999 nodes or elements is a WriteError (write MED instead).
• Coordinates are written as %.16E, which round-trips a double exactly. Every line stays within 80 columns: a record that would cross column 80 continues on an indented next line.
• Group names are sanitised for Code_Aster. Anything but ASCII letters, digits and _ becomes _, and the name is truncated to 24 characters. A name that then collides with an earlier one of the same kind gets _1, _2, …. Each change gets a warning.
• Dropped, with a warning and a provenance note: side regions (.mail has no facet group) and every data array (a .mail mesh has none). A cell type with no keyword (polygons, polyhedra, higher-order Lagrange cells) is a WriteError.

Errors

These follow Code_Aster, where each is fatal. A node or element name defined twice, an element or group that names an undefined node or element, a block with no FINSF, a coordinate that is not a number, or a token where a keyword should be all raise ReadError, naming the culprit and its line. A group listing the same member twice gets a warning, and the member is kept once. A file with no FIN is read to the end with a warning.

Notes

• The names in the file are not kept. A .mail → .mail round trip renames nodes and elements N…/M…, so a command file (.comm) that refers to individual nodes by name needs the groups instead, which are kept.
• Connectivity is read as written, never reoriented. Code_Aster accepts meshes whose volume cells are all mirrored (a few of its own test meshes are). Such a mesh reads fine, and attach_quality flags its cells as quality:inverted.
• Code_Aster drops an empty group. meshio++ keeps it as an empty region, as it does for every format.
• TRIA7 needed a new cell type, triangle7 (v16.0.0); see cell types.
• Not read: .comm command files, and results. Code_Aster writes results as MED (.rmed), which the MED reader handles.

The syntax reference is U3.01.00, The Code_Aster mesh file. The reader's and writer's rules above come from Code_Aster's source (bibfor/modelisa/lrmast.F90, lirlig.F90, stkcoo.F90, and bibfor/stbtrias/ for its writer).