:orphan:
# MatCreateMPIAIJWithArrays
creates a `MATMPIAIJ` matrix using arrays that contain in standard CSR format for the local rows. 
## Synopsis
```
#include "petscmat.h" 
PetscErrorCode MatCreateMPIAIJWithArrays(MPI_Comm comm, PetscInt m, PetscInt n, PetscInt M, PetscInt N, const PetscInt i[], const PetscInt j[], const PetscScalar a[], Mat *mat)
```
Collective


## Input Parameters

- ***comm -*** MPI communicator
- ***m -*** number of local rows (Cannot be `PETSC_DECIDE`)
- ***n -*** This value should be the same as the local size used in creating the
x vector for the matrix-vector product y = Ax. (or `PETSC_DECIDE` to have
calculated if N is given) For square matrices n is almost always m.
- ***M -*** number of global rows (or `PETSC_DETERMINE` to have calculated if m is given)
- ***N -*** number of global columns (or `PETSC_DETERMINE` to have calculated if n is given)
- ***i -*** row indices; that is i[0] = 0, i[row] = i[row-1] + number of elements in that row of the matrix
- ***j -*** column indices
- ***a -*** optional matrix values



## Output Parameter

- ***mat -*** the matrix





## Notes
The `i`, `j`, and `a` arrays ARE copied by this routine into the internal format used by PETSc;
thus you CANNOT change the matrix entries by changing the values of a[] after you have
called this routine. Use `MatCreateMPIAIJWithSplitArrays()` to avoid needing to copy the arrays.

The `i` and `j` indices are 0 based, and `i` indices are indices corresponding to the local `j` array.

The format which is used for the sparse matrix input, is equivalent to a
row-major ordering.. i.e for the following matrix, the input data expected is
as shown

Once you have created the matrix you can update it with new numerical values using MatUpdateMPIAIJWithArrays
```none
        1 0 0
        2 0 3     P0
       -------
        4 5 6     P1

     Process0 [P0] rows_owned=[0,1]
        i =  {0,1,3}  [size = nrow+1  = 2+1]
        j =  {0,0,2}  [size = 3]
        v =  {1,2,3}  [size = 3]

     Process1 [P1] rows_owned=[2]
        i =  {0,3}    [size = nrow+1  = 1+1]
        j =  {0,1,2}  [size = 3]
        v =  {4,5,6}  [size = 3]
```



## See Also
 [](ch_matrices), `Mat`, `MATMPIAIK`, `MatCreate()`, `MatCreateSeqAIJ()`, `MatSetValues()`, `MatMPIAIJSetPreallocation()`, `MatMPIAIJSetPreallocationCSR()`,
`MATMPIAIJ`, `MatCreateAIJ()`, `MatCreateMPIAIJWithSplitArrays()`, `MatUpdateMPIAIJWithArrays()`

## Level
intermediate

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/aij/mpi/mpiaij.c.html#MatCreateMPIAIJWithArrays">src/mat/impls/aij/mpi/mpiaij.c</A>


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


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