:orphan:
# MatXAIJSetPreallocation
set preallocation for serial and parallel `MATAIJ`, `MATBAIJ`, and `MATSBAIJ` matrices and their unassembled versions. 
## Synopsis
```
#include "petscmat.h"  
PetscErrorCode MatXAIJSetPreallocation(Mat A, PetscInt bs, const PetscInt dnnz[], const PetscInt onnz[], const PetscInt dnnzu[], const PetscInt onnzu[])
```
Collective


## Input Parameters

- ***A -*** matrix being preallocated
- ***bs -*** block size
- ***dnnz -*** number of nonzero column blocks per block row of diagonal part of parallel matrix
- ***onnz -*** number of nonzero column blocks per block row of off-diagonal part of parallel matrix
- ***dnnzu -*** number of nonzero column blocks per block row of upper-triangular part of diagonal part of parallel matrix
- ***onnzu -*** number of nonzero column blocks per block row of upper-triangular part of off-diagonal part of parallel matrix





## See Also
 [](ch_matrices), `Mat`, `MatSeqAIJSetPreallocation()`, `MatMPIAIJSetPreallocation()`, `MatSeqBAIJSetPreallocation()`, `MatMPIBAIJSetPreallocation()`,
`MatSeqSBAIJSetPreallocation()`, `MatMPISBAIJSetPreallocation()`,
`PetscSplitOwnership()`

## Level
beginner

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/utils/gcreate.c.html#MatXAIJSetPreallocation">src/mat/utils/gcreate.c</A>


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


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