PCSPAISetBlockSize#

set the block size for the PCSPAI preconditioner

Synopsis#

#include "petscpc.h" 
PetscErrorCode PCSPAISetBlockSize(PC pc, PetscInt block_size1)

Input Parameters#

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.