#include "petscmat.h" PetscErrorCode PETSCMAT_DLLEXPORT MatMPIBAIJSetPreallocation(Mat B,PetscInt bs,PetscInt d_nz,const PetscInt d_nnz,PetscInt o_nz,const PetscInt o_nnz)Collective on Mat
|A||- the matrix|
|bs||- size of blockk|
|d_nz||- number of block nonzeros per block row in diagonal portion of local submatrix (same for all local rows)|
|d_nnz||- array containing the number of block nonzeros in the various block rows of the in diagonal portion of the local (possibly different for each block row) or PETSC_NULL. You must leave room for the diagonal entry even if it is zero.|
|o_nz||- number of block nonzeros per block row in the off-diagonal portion of local submatrix (same for all local rows).|
|o_nnz||- array containing the number of nonzeros in the various block rows of the off-diagonal portion of the local submatrix (possibly different for each block row) or PETSC_NULL.|
If the *_nnz parameter is given then the *_nz parameter is ignored
|-mat_block_size||- size of the blocks to use|
|-mat_use_hash_table <fact>||- Notes: If PETSC_DECIDE or PETSC_DETERMINE is used for a particular argument on one processor than it must be used on all processors that share the object for that argument.|
The user can specify preallocated storage for the diagonal part of the local submatrix with either d_nz or d_nnz (not both). Set d_nz=PETSC_DEFAULT and d_nnz=PETSC_NULL for PETSc to control dynamic memory allocation. Likewise, specify preallocated storage for the off-diagonal part of the local submatrix with o_nz or o_nnz (not both).
Consider a processor that owns rows 3, 4 and 5 of a parallel matrix. In the figure below we depict these three local rows and all columns (0-11).
0 1 2 3 4 5 6 7 8 9 10 11 ------------------- row 3 | o o o d d d o o o o o o row 4 | o o o d d d o o o o o o row 5 | o o o d d d o o o o o o -------------------
Thus, any entries in the d locations are stored in the d (diagonal) submatrix, and any entries in the o locations are stored in the o (off-diagonal) submatrix. Note that the d and the o submatrices are stored simply in the MATSEQBAIJ format for compressed row storage.
Now d_nz should indicate the number of block nonzeros per row in the d matrix, and o_nz should indicate the number of block nonzeros per row in the o matrix. In general, for PDE problems in which most nonzeros are near the diagonal, one expects d_nz >> o_nz. For large problems you MUST preallocate memory or you will get TERRIBLE performance; see the users' manual chapter on matrices.
|  MatMPIBAIJSetPreallocation(Mat A,PetscInt bs,const PetscInt nnz,const PetscInt onz)||->||MatMPIBAIJSetPreallocation(A,bs,0,nnz,0,onz)|
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