petsc-3.7.1 2016-05-15
Report Typos and Errors

# MatCreateBAIJ

Creates a sparse parallel matrix in block AIJ format (block compressed row). For good matrix assembly performance the user should preallocate the matrix storage by setting the parameters d_nz (or d_nnz) and o_nz (or o_nnz). By setting these parameters accurately, performance can be increased by more than a factor of 50.

### Synopsis

    #include "petscmat.h"
    PetscErrorCode  MatCreateBAIJ(MPI_Comm comm,PetscInt bs,PetscInt m,PetscInt n,PetscInt M,PetscInt N,PetscInt d_nz,const PetscInt d_nnz[],PetscInt o_nz,const PetscInt o_nnz[],Mat *A)

Collective on MPI_Comm Many br

### Input Parameters

| comm | - MPI communicator Many br
| bs | - size of block, the blocks are ALWAYS square. One can use MatSetBlockSizes() to set a different row and column blocksize but the row Many brblocksize always defines the size of the blocks. The column blocksize sets the blocksize of the vectors obtained with MatCreateVecs() Many br
| m | - number of local rows (or PETSC_DECIDE to have calculated if M is given) Many brThis value should be the same as the local size used in creating the Many bry vector for the matrix-vector product y = Ax. Many br
| n | - number of local columns (or PETSC_DECIDE to have calculated if N is given) Many brThis value should be the same as the local size used in creating the Many brx vector for the matrix-vector product y = Ax. Many br
| M | - number of global rows (or PETSC_DETERMINE to have calculated if m is given) Many br
| N | - number of global columns (or PETSC_DETERMINE to have calculated if n is given) Many br
| d_nz | - number of nonzero blocks per block row in diagonal portion of local Many brsubmatrix (same for all local rows) Many br
| d_nnz | - array containing the number of nonzero blocks in the various block rows Many brof the in diagonal portion of the local (possibly different for each block Many brrow) or NULL. If you plan to factor the matrix you must leave room for the diagonal entry Many brand set it even if it is zero. Many br
| o_nz | - number of nonzero blocks per block row in the off-diagonal portion of local Many brsubmatrix (same for all local rows). Many br
| o_nnz | - array containing the number of nonzero blocks in the various block rows of the Many broff-diagonal portion of the local submatrix (possibly different for Many breach block row) or NULL. Many br

### Output Parameter

A -the matrix Many br

### Options Database Keys

| -mat_block_size | - size of the blocks to use Many br
| -mat_use_hash_table <fact> | - Many brIt is recommended that one use the MatCreate(), MatSetType() and/or MatSetFromOptions(), Many brMatXXXXSetPreallocation() paradgm instead of this routine directly. Many br[MatXXXXSetPreallocation() is, for example, MatSeqAIJSetPreallocation] Many br

### Notes

If the *_nnz parameter is given then the *_nz parameter is ignored Many br

A nonzero block is any block that as 1 or more nonzeros in it Many br

The user MUST specify either the local or global matrix dimensions Many br(possibly both). Many br

If PETSC_DECIDE or PETSC_DETERMINE is used for a particular argument on one processor Many brthan it must be used on all processors that share the object for that argument. Many br

### Storage Information

For a square global matrix we define each processor's diagonal portion Many brto be its local rows and the corresponding columns (a square submatrix); Many breach processor's off-diagonal portion encompasses the remainder of the Many brlocal matrix (a rectangular submatrix). Many br

The user can specify preallocated storage for the diagonal part of Many brthe local submatrix with either d_nz or d_nnz (not both). Set Many brd_nz=PETSC_DEFAULT and d_nnz=NULL for PETSc to control dynamic Many brmemory allocation. Likewise, specify preallocated storage for the Many broff-diagonal part of the local submatrix with o_nz or o_nnz (not both). Many br

Consider a processor that owns rows 3, 4 and 5 of a parallel matrix. In Many brthe figure below we depict these three local rows and all columns (0-11). Many br

               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
              --------------------------

Many br

Thus, any entries in the d locations are stored in the d (diagonal) Many brsubmatrix, and any entries in the o locations are stored in the Many bro (off-diagonal) submatrix. Note that the d and the o submatrices are Many brstored simply in the MATSEQBAIJ format for compressed row storage. Many br

Now d_nz should indicate the number of block nonzeros per row in the d matrix, Many brand o_nz should indicate the number of block nonzeros per row in the o matrix. Many brIn general, for PDE problems in which most nonzeros are near the diagonal, Many brone expects d_nz >> o_nz. For large problems you MUST preallocate memory Many bror you will get TERRIBLE performance; see the users' manual chapter on Many brmatrices. Many br

Many br

### Keywords

matrix, block, aij, compressed row, sparse, parallel

### See Also

MatCreate(), MatCreateSeqBAIJ(), MatSetValues(), MatCreateBAIJ(), MatMPIBAIJSetPreallocation(), MatMPIBAIJSetPreallocationCSR()

Level:intermediate
Location:src/mat/impls/baij/mpi/mpibaij.c
Index of all Mat routines
Table of Contents for all manual pages
Index of all manual pages