# Preconditioners for MLFMM

A number of preconditioners are available when using the multilevel fast multipole method (MLFMM) (for advanced users only).

- Block-Jacobi using LU-decomposition (64)
- Preconditioner for an MLFMM solution where the inverses of the preconditioner are calculated and applied during every iteration step.
- Incomplete LU decomposition (ILU) (128)
- Preconditioner for an MLFMM solution that uses an incomplete LU-decomposition of the matrix.
- 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 system.
When using the parallel Solver, the factorisation type can be specified.

- Block-Jacobi preconditioner of MLFMM one-level-up (4096)
- Preconditioner for an MLFMM solution that uses LU-decomposition on entries in the boxes, one-level-up from the finest boxes.
- Sparse approximate inverse (SPAI) (8192)
- Preconditioner for an MLFMM solution.

- Sparse LU (8193)
- Preconditioner for an MLFMM solution that uses a
sparse LU decomposition of the MLFMM near field
matrix.
When using the parallel Solver, the factorisation type can be specified.

_{3}field at the CG card.