#include "petscpc.h" PetscErrorCode PCSPAISetBlockSize(PC pc,int block_size1)
|pc||- the preconditioner|
|n||- block size (default 1)|
Notes: A block size of 1 treats A as a matrix of scalar elements. A block size of s > 1 treats A as a matrix of sxs blocks. A block size of 0 treats A as a matrix with variable sized blocks, which are determined by searching for dense square diagonal blocks in A. This can be very effective for finite-element matrices.
SPAI will convert A to block form, use a block version of the preconditioner algorithm, and then convert the result back to scalar form.
In many cases the a block-size parameter other than 1 can lead to very significant improvement in performance.