# MatHYPRESetPreallocation
Preallocates memory for a sparse parallel matrix in HYPRE IJ format 
## Synopsis
```
PetscErrorCode MatHYPRESetPreallocation(Mat A, PetscInt dnz, const PetscInt dnnz[], PetscInt onz, const PetscInt onnz[])
```
Collective


## Input Parameters

- ***A -*** the matrix
- ***dnz  -*** number of nonzeros per row in DIAGONAL portion of local submatrix
(same value is used for all local rows)
- ***dnnz -*** array containing the number of nonzeros in the various rows of the
DIAGONAL portion of the local submatrix (possibly different for each row)
or NULL (`PETSC_NULL_INTEGER` in Fortran), if d_nz is used to specify the nonzero structure.
The size of this array is equal to the number of local rows, i.e 'm'.
For matrices that will be factored, you must leave room for (and set)
the diagonal entry even if it is zero.
- ***onz  -*** number of nonzeros per row in the OFF-DIAGONAL portion of local
submatrix (same value is used for all local rows).
- ***onnz -*** array containing the number of nonzeros in the various rows of the
OFF-DIAGONAL portion of the local submatrix (possibly different for
each row) or NULL (`PETSC_NULL_INTEGER` in Fortran), if o_nz is used to specify the nonzero
structure. The size of this array is equal to the number
of local rows, i.e 'm'.



## Note
If the *nnz parameter is given then the *nz parameter is ignored; for sequential matrices, onz and onnz are ignored.




## See Also
 `MatCreate()`, `MatMPIAIJSetPreallocation()`, `MATHYPRE`

## Level
intermediate

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/hypre/mhypre.c.html#MatHYPRESetPreallocation">src/mat/impls/hypre/mhypre.c</A>

## Examples
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex4.c.html">src/ksp/ksp/tutorials/ex4.c.html</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex55.c.html">src/ksp/ksp/tutorials/ex55.c.html</A><BR>

## Implementations

<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/hypre/mhypre.c.html#MatHYPRESetPreallocation_HYPRE">MatHYPRESetPreallocation_HYPRE in src/mat/impls/hypre/mhypre.c</A><BR>


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[Edit on GitLab](https://gitlab.com/petsc/petsc/-/edit/release/src/mat/impls/hypre/mhypre.c)


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