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# MatPreallocateSet
Indicates the locations (rows and columns) in the matrix where nonzeros will be inserted using a local number of the rows and columns 
## Synopsis
```
#include <petscmat.h>
PetscErrorCode MatPreallocateSet(PetscInt nrows, PetscInt *rows,PetscInt ncols, PetscInt *cols,PetscInt *dnz, PetscInt *onz)
```
Not Collective


## Input Parameters

- ***row -*** the row
- ***ncols -*** the number of columns in the matrix
- ***cols -*** the columns indicated



## Output Parameters

- ***dnz -*** the array that will be passed to the matrix preallocation routines
- ***onz -*** the other array passed to the matrix preallocation routines


 (since v3.19)


## Notes
This routine is no longer needed since assembling matrices without explicit preallocation will not be slower than
the use of this routine

Do not malloc or free `dnz` and `onz` that is handled internally by these routines

This is a MACRO not a function because it uses variables declared in MatPreallocateBegin().


## See Also
 [](ch_matrices), `MatPreallocateEnd()`, `MatPreallocateSet()`, `MatPreallocateSymmetricSetBlock()`
`MatPreallocateBegin()`, `MatPreallocateSetLocal()`

## Level
deprecated

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/include/petscmat.h.html#MatPreallocateSet">include/petscmat.h</A>


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