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For the ** three-dimensional** case, it corresponds to:

- generating meshes from point, two-dimensional meshes, coarse meshes, etc., data, using the appropriate algorithms;
- modifying existing meshes and combining them to form the final mesh, step by step, to which a
D.S. of type
**NOPO**is associated. This D.S. is then stored in a sequential access file.

In order to perform the above steps, we need to:

- locate all the
*primal*sub-sets in the domain by eliminating all sub-sets which can be derived by symmetry, translation, etc., or more generally, by geometric transformation; - locate the domains which can be derived from a two-dimensional mesh of one of its sections;
- record, furthermore, the primal subsets linked to physical type constraints;
- search for the module which is the most suitable for each of these sub-sets;
- determine the nature of the data which each of these modules use;
- construct the data from the points, ..., present;
- activate the desired mesh generator(s);
- perform the symmetries, translations, rotations, etc., of the primal sub-sets;
- "glue" these meshes together, two by two;
- repeat the two previous steps until the entire domain is covered;
- split the elements into tetrahedra or into sub-elements of the same type, if desired;
- define the non-vertex nodes, if necessary, and remove the vertices from the nodal list;
- renumber, if necessary, the elements and/or nodes;
- store the result on file (and plot it to verify and ensure the quality of the mesh).

For each primal sub-set, we select the module which is most suitable:

- for a topologically hexahedral domain, we use, excluding
**APNOP3**, module**GEL3D1**(see chapter 3); - For a topologically cylindrical domain, we use module
**MA2D3D**(see chapter 3, or keyword**MA23**of**APNOP3**); - for an arbitrary domain, module
**COLIB2**(multi-block method), or the corresponding processor**COLIXX**, is used excluding**APNOP3**(see chapter 3); - when the elements to be created are few or identical, module
**CONOPO**(manual method) could be used; - module
**MAOBJE**is used to treat catalogued objects; - for all cases where the mesh is created not using
**APNOP3**, if the mesh must be used for fine manipulations,**SDREST**is used to introduce this mesh into memory and manipulate it via the different possibilities presented by**APNOP3**.