#include "petscmat.h" PetscErrorCode MatSeqBAIJSetPreallocation(Mat B,PetscInt bs,PetscInt nz,const PetscInt nnz)Collective
|B||- the matrix|
|bs||- size of block, the blocks are ALWAYS square. One can use MatSetBlockSizes() to set a different row and column blocksize but the row blocksize always defines the size of the blocks. The column blocksize sets the blocksize of the vectors obtained with MatCreateVecs()|
|nz||- number of block nonzeros per block row (same for all rows)|
|nnz||- array containing the number of block nonzeros in the various block rows (possibly different for each block row) or NULL|
|-mat_no_unroll||- uses code that does not unroll the loops in the block calculations (much slower)|
|-mat_block_size||- size of the blocks to use|
You can call MatGetInfo() to get information on how effective the preallocation was; for example the fields mallocs,nz_allocated,nz_used,nz_unneeded; You can also run with the option -info and look for messages with the string malloc in them to see if additional memory allocation was needed.
The block AIJ format is fully compatible with standard Fortran 77 storage. That is, the stored row and column indices can begin at either one (as in Fortran) or zero. See the users' manual for details.
Specify the preallocated storage with either nz or nnz (not both). Set nz=PETSC_DEFAULT and nnz=NULL for PETSc to control dynamic memory allocation. See Users-Manual: ch_mat for details.