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# MatCompositeMerge
Given a composite matrix, replaces it with a "regular" matrix by summing or computing the product of all the matrices inside the composite matrix. 
## Synopsis
```
#include "petscmat.h" 
PetscErrorCode MatCompositeMerge(Mat mat)
```
Collective


## Input Parameter

- ***mat -*** the composite matrix



## Options Database Keys

- ***-mat_composite_merge -*** merge in `MatAssemblyEnd()`
- ***-mat_composite_merge_type -*** set merge direction





## Note
The `MatType` of the resulting matrix will be the same as the `MatType` of the FIRST matrix in the composite matrix.


## See Also
 [](ch_matrices), `Mat`, `MatDestroy()`, `MatMult()`, `MatCompositeAddMat()`, `MatCreateComposite()`, `MatCompositeSetMatStructure()`, `MatCompositeSetMergeType()`, `MATCOMPOSITE`

## Level
advanced

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/composite/mcomposite.c.html#MatCompositeMerge">src/mat/impls/composite/mcomposite.c</A>

## Examples
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/tutorials/ex9.c.html">src/mat/tutorials/ex9.c</A><BR>

## Implementations

<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/composite/mcomposite.c.html#MatCompositeMerge_Composite">MatCompositeMerge_Composite in src/mat/impls/composite/mcomposite.c</A><BR>


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


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