:orphan:
# MatGetDiagonalBlock
Returns the part of the matrix associated with the on-process coupling
## Synopsis
```
#include "petscmat.h"
PetscErrorCode MatGetDiagonalBlock(Mat A, Mat *a)
```
Not Collective
## Input Parameter
- ***A -*** the matrix
## Output Parameter
- ***a -*** the diagonal part (which is a SEQUENTIAL matrix)
## Notes
See `MatCreateAIJ()` for more information on the "diagonal part" of the matrix.
Use caution, as the reference count on the returned matrix is not incremented and it is used as part of `A`'s normal operation.
## See Also
[](ch_matrices), `Mat`, `MatCreateAIJ()`, `MATAIJ`, `MATBAIJ`, `MATSBAIJ`
## Level
advanced
## Location
src/mat/interface/matrix.c
## Examples
src/ksp/ksp/tutorials/ex76.c
## Implementations
MatGetDiagonalBlock_MPIAIJ in src/mat/impls/aij/mpi/mpiaijpc.c
MatGetDiagonalBlock_MPIBAIJ in src/mat/impls/baij/mpi/mpibaij.c
MatGetDiagonalBlock_MPIDense in src/mat/impls/dense/mpi/mpidense.c
MatGetDiagonalBlock_Htool in src/mat/impls/htool/htool.cxx
MatGetDiagonalBlock_IS in src/mat/impls/is/matis.c
MatGetDiagonalBlock_MPIKAIJ in src/mat/impls/kaij/kaij.c
MatGetDiagonalBlock_Normal in src/mat/impls/normal/normm.c
MatGetDiagonalBlock_NormalHermitian in src/mat/impls/normal/normmh.c
MatGetDiagonalBlock_MPISBAIJ in src/mat/impls/sbaij/mpi/mpisbaij.c
MatGetDiagonalBlock_MPISELL in src/mat/impls/sell/mpi/mpisell.c
---
[Edit on GitLab](https://gitlab.com/petsc/petsc/-/edit/release/src/mat/interface/matrix.c)
[Index of all Mat routines](index.md)
[Table of Contents for all manual pages](/manualpages/index.md)
[Index of all manual pages](/manualpages/singleindex.md)