# Preconditioners for FEM

A few preconditioners are available for the finite element method (FEM).

- It is recommended to use the default settings. Changing the preconditioner is recommended only for advanced users.
- The number in brackets corresponds to the value of the I
_{3}field at the CG card in the model .pre file.

- Multilevel ILU/diagonal decomposition (512)
- Preconditioner for a hybrid FEM/MoM solution that uses a multilevel sparse incomplete LU-decomposition with threshold and controlled fill-in. Note, not available for parallel.
- Multilevel FEM-MLFMM LU/diagonal decomposition (2010)
- Preconditioner for a hybrid FEM/MLFMM solution that uses a multilevel sparse LU decomposition
of the combined and partitioned, FEM/MLFMM system. This is the default for a FEM/MLFMM solution.
When using the parallel Solver, the factorisation type, which slightly impacts runtime and memory, can be specified.

- Multilevel LU/diagonal decomposition (2050)
- Preconditioner for a hybrid FEM/MoM solution that uses a multilevel sparse LU decomposition of
the partitioned system. This is the default for a FEM/MoM solution.
When using the parallel Solver, the factorisation type, which slightly impacts runtime and memory, can be specified.