Go back

Maps

The construction of a Finite Element space requires the definition of the degrees of freedom (DOFs) that depend on the geometrical shape of the element and the polynomial degree. For parallel runs, each process creates its own list of DOFs according to a local numbering scheme. In this way, each process is able to build the matrices and vectors associated with the corresponding local mesh. An issue arises when considering the DOFs belonging to the interface between two processes. To avoid that both the processes operate on the same DOFs, only one of them will own the DOFs at the interface.

However, for each process, it is necessary to create a map that links the local numbering of the DOFs to a global numbering that is common to all the processes. Actually, this procedure generates two local-to-global maps:

• a unique map;
• a repeated map.

The unique map contains only the DOFs owned by the process and it is used for operating on matrices or vectors that do not require communication among the processes.

The repeated map contains not only the DOFs owned by the process but also all the DOFs at the interface (that may not be owned by the process). This map is used when assembling the linear system.