PETSc version 3.17.4
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# MatCreateSeqSBAIJ

Creates a sparse symmetric matrix in block AIJ (block compressed row) format. For good matrix assembly performance the user should preallocate the matrix storage by setting the parameter nz (or the array nnz). By setting these parameters accurately, performance during matrix assembly can be increased by more than a factor of 50.

### Synopsis

    #include "petscmat.h"
    PetscErrorCode  MatCreateSeqSBAIJ(MPI_Comm comm,PetscInt bs,PetscInt m,PetscInt n,PetscInt nz,const PetscInt nnz[],Mat *A)

Collective

### Input Parameters

| comm | - MPI communicator, set to PETSC_COMM_SELF
| 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()
| m | - number of rows, or number of columns
| nz | - number of block nonzeros per block row (same for all rows)
| nnz | - array containing the number of block nonzeros in the upper triangular plus diagonal portion of each block (possibly different for each block row) or NULL

### Output Parameter

| A | - the symmetric matrix

### Options Database Keys

| -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

It is recommended that one use the MatCreate(), MatSetType() and/or MatSetFromOptions(), MatXXXXSetPreallocation() paradigm instead of this routine directly. [MatXXXXSetPreallocation() is, for example, MatSeqAIJSetPreallocation]

### Notes

The number of rows and columns must be divisible by blocksize. This matrix type does not support complex Hermitian operation.

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.

If the nnz parameter is given then the nz parameter is ignored

### See Also

MatCreate(), MatCreateSeqAIJ(), MatSetValues(), MatCreateSBAIJ()

### Level

intermediate

### Location

src/mat/impls/sbaij/seq/sbaij.c
Index of all Mat routines
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Index of all manual pages