The -optim option allows to preserve the initial sizes of the mesh edges in order to improve the mesh quality without modifying the edge lengths.
The prescribed size at a mesh vertex is computed (by the MMG3D_DoSol API function) as the mean of the lengths of the edges passing through this vertex.
Note that we preserve the mean of the edge lengths at vertices: thus, if the edges passing through a vertex have very different sizes, the resulting mesh may be far from the initial one.
This option is useless if you provide a sizemap with your mesh.
Example(s): mmg3d_opt1.
