PCILU

Incomplete factorization preconditioners.

	-pc_factor_levels <k>	- number of levels of fill for ILU(k)
	-pc_factor_in_place	- only for ILU(0) with natural ordering, reuses the space of the matrix for its factorization (overwrites original matrix)
	-pc_factor_diagonal_fill	- fill in a zero diagonal even if levels of fill indicate it wouldn't be fill
	-pc_factor_reuse_ordering	- reuse ordering of factorized matrix from previous factorization
	-pc_factor_use_drop_tolerance <dt,dtcol,maxrowcount>	- use Saad's drop tolerance ILUdt
	-pc_factor_fill <nfill>	- expected amount of fill in factored matrix compared to original matrix, nfill > 1
	-pc_factor_nonzeros_along_diagonal	- reorder the matrix before factorization to remove zeros from the diagonal, this decreases the chance of getting a zero pivot
	-pc_factor_mat_ordering_type <natural,nd,1wd,rcm,qmd>	- set the row/column ordering of the factored matrix
	-pc_factor_pivot_in_blocks	- for block ILU(k) factorization, i.e. with BAIJ matrices with block size larger than 1 the diagonal blocks are factored with partial pivoting (this increases the stability of the ILU factorization
	-pc_factor_shift_nonzero <shift>	- Sets shift amount or PETSC_DECIDE for the default
	-pc_factor_shift_positive_definite [PETSC_TRUE/PETSC_FALSE]	- Activate/Deactivate PCFactorSetShiftPd(); the value is optional with PETSC_TRUE being the default

Notes: Only implemented for some matrix formats. Not implemented in parallel

For BAIJ matrices this implements a point block ILU