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# MatResetPreallocation
Reset matrix to use the original nonzero pattern provided by users. 
## Synopsis
```
#include "petscmat.h" 
PetscErrorCode MatResetPreallocation(Mat A)
```
Collective


## Input Parameter

- ***A -*** the matrix





## Notes
The allocated memory will be shrunk after calling `MatAssemblyBegin()` and `MatAssemblyEnd()` with `MAT_FINAL_ASSEMBLY`.

Users can reset the preallocation to access the original memory.

Currently only supported for  `MATAIJ` matrices.


## See Also
 [](ch_matrices), `Mat`, `MatSeqAIJSetPreallocation()`, `MatMPIAIJSetPreallocation()`, `MatXAIJSetPreallocation()`

## Level
beginner

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/interface/matrix.c.html#MatResetPreallocation">src/mat/interface/matrix.c</A>

## Examples
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/tutorials/ex4.c.html">src/mat/tutorials/ex4.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/tutorials/ex4f.F90.html">src/mat/tutorials/ex4f.F90</A><BR>

## Implementations

<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/aij/mpi/mpiaij.c.html#MatResetPreallocation_MPIAIJ">MatResetPreallocation_MPIAIJ in src/mat/impls/aij/mpi/mpiaij.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/aij/seq/aij.c.html#MatResetPreallocation_SeqAIJ">MatResetPreallocation_SeqAIJ in src/mat/impls/aij/seq/aij.c</A><BR>


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