:orphan:
# MatAssemblyBegin
Begins assembling the matrix.  This routine should be called after completing all calls to `MatSetValues()`. 
## Synopsis
```
#include "petscmat.h" 
PetscErrorCode MatAssemblyBegin(Mat mat, MatAssemblyType type)
```
Collective


## Input Parameters

- ***mat -*** the matrix
- ***type -*** type of assembly, either `MAT_FLUSH_ASSEMBLY` or `MAT_FINAL_ASSEMBLY`





## Notes
`MatSetValues()` generally caches the values that belong to other MPI ranks.  The matrix is ready to
use only after `MatAssemblyBegin()` and `MatAssemblyEnd()` have been called.

Use `MAT_FLUSH_ASSEMBLY` when switching between `ADD_VALUES` and `INSERT_VALUES`
in `MatSetValues()`; use `MAT_FINAL_ASSEMBLY` for the final assembly before
using the matrix.

ALL processes that share a matrix MUST call `MatAssemblyBegin()` and `MatAssemblyEnd()` the SAME NUMBER of times, and each time with the
same flag of `MAT_FLUSH_ASSEMBLY` or `MAT_FINAL_ASSEMBLY` for all processes. Thus you CANNOT locally change from `ADD_VALUES` to `INSERT_VALUES`, that is
a global collective operation requiring all processes that share the matrix.

Space for preallocated nonzeros that is not filled by a call to `MatSetValues()` or a related routine are compressed
out by assembly. If you intend to use that extra space on a subsequent assembly, be sure to insert explicit zeros
before `MAT_FINAL_ASSEMBLY` so the space is not compressed out.


## See Also
 [](ch_matrices), `Mat`, `MatAssemblyEnd()`, `MatSetValues()`, `MatAssembled()`

## Level
beginner

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

## Examples
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/impls/stag/tutorials/ex1.c.html">src/dm/impls/stag/tutorials/ex1.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/impls/stag/tutorials/ex2.c.html">src/dm/impls/stag/tutorials/ex2.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/impls/stag/tutorials/ex3.c.html">src/dm/impls/stag/tutorials/ex3.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/impls/stag/tutorials/ex4.c.html">src/dm/impls/stag/tutorials/ex4.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/impls/stag/tutorials/ex8.c.html">src/dm/impls/stag/tutorials/ex8.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex1.c.html">src/ksp/ksp/tutorials/ex1.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex11.c.html">src/ksp/ksp/tutorials/ex11.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex11f.F90.html">src/ksp/ksp/tutorials/ex11f.F90</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex12.c.html">src/ksp/ksp/tutorials/ex12.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex13.c.html">src/ksp/ksp/tutorials/ex13.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex13f90.F90.html">src/ksp/ksp/tutorials/ex13f90.F90</A><BR>

## Implementations

<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/adj/mpi/mpiadj.c.html#MatAssemblyBegin_MPIAdj">MatAssemblyBegin_MPIAdj in src/mat/impls/adj/mpi/mpiadj.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/aij/mpi/mpiaij.c.html#MatAssemblyBegin_MPIAIJ">MatAssemblyBegin_MPIAIJ in src/mat/impls/aij/mpi/mpiaij.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/baij/mpi/mpibaij.c.html#MatAssemblyBegin_MPIBAIJ">MatAssemblyBegin_MPIBAIJ in src/mat/impls/baij/mpi/mpibaij.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/dense/mpi/mpidense.c.html#MatAssemblyBegin_MPIDense">MatAssemblyBegin_MPIDense in src/mat/impls/dense/mpi/mpidense.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/dense/seq/dense.c.html#MatAssemblyBegin_SeqDense">MatAssemblyBegin_SeqDense in src/mat/impls/dense/seq/dense.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/elemental/matelem.cxx.html#MatAssemblyBegin_Elemental">MatAssemblyBegin_Elemental in src/mat/impls/elemental/matelem.cxx</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/hypre/mhypre.c.html#MatAssemblyBegin_HYPRE">MatAssemblyBegin_HYPRE in src/mat/impls/hypre/mhypre.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/is/matis.c.html#MatAssemblyBegin_IS">MatAssemblyBegin_IS in src/mat/impls/is/matis.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/nest/matnest.c.html#MatAssemblyBegin_Nest">MatAssemblyBegin_Nest in src/mat/impls/nest/matnest.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/preallocator/matpreallocator.c.html#MatAssemblyBegin_Preallocator">MatAssemblyBegin_Preallocator in src/mat/impls/preallocator/matpreallocator.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/sbaij/mpi/mpisbaij.c.html#MatAssemblyBegin_MPISBAIJ">MatAssemblyBegin_MPISBAIJ in src/mat/impls/sbaij/mpi/mpisbaij.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/scalapack/matscalapack.c.html#MatAssemblyBegin_ScaLAPACK">MatAssemblyBegin_ScaLAPACK in src/mat/impls/scalapack/matscalapack.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/sell/mpi/mpisell.c.html#MatAssemblyBegin_MPISELL">MatAssemblyBegin_MPISELL in src/mat/impls/sell/mpi/mpisell.c</A><BR>


---
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