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# MatZeroEntries
Zeros all entries of a matrix.  For sparse matrices this routine retains the old nonzero structure. 
## Synopsis
```
#include "petscmat.h" 
PetscErrorCode MatZeroEntries(Mat mat)
```
Logically Collective


## Input Parameter

- ***mat -*** the matrix





## Note
If the matrix was not preallocated then a default, likely poor preallocation will be set in the matrix, so this should be called after the preallocation phase.
See the Performance chapter of the users manual for information on preallocating matrices.


## See Also
 [](ch_matrices), `Mat`, `MatZeroRows()`, `MatZeroRowsColumns()`

## Level
intermediate

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

## Examples
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex42.c.html">src/ksp/ksp/tutorials/ex42.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex43.c.html">src/ksp/ksp/tutorials/ex43.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex49.c.html">src/ksp/ksp/tutorials/ex49.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex5.c.html">src/ksp/ksp/tutorials/ex5.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex59.c.html">src/ksp/ksp/tutorials/ex59.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex5f.F90.html">src/ksp/ksp/tutorials/ex5f.F90</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex67.c.html">src/ksp/ksp/tutorials/ex67.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex70.c.html">src/ksp/ksp/tutorials/ex70.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex73.c.html">src/ksp/ksp/tutorials/ex73.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex77.c.html">src/ksp/ksp/tutorials/ex77.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex77f.F90.html">src/ksp/ksp/tutorials/ex77f.F90</A><BR>

## Implementations

<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/impls/da/hypre/mhyp.c.html#MatZeroEntries_HYPREStruct">MatZeroEntries_HYPREStruct in src/dm/impls/da/hypre/mhyp.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/impls/da/hypre/mhyp.c.html#MatZeroEntries_HYPRESStruct">MatZeroEntries_HYPRESStruct in src/dm/impls/da/hypre/mhyp.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/aij/mpi/mpiaij.c.html#MatZeroEntries_MPIAIJ">MatZeroEntries_MPIAIJ in src/mat/impls/aij/mpi/mpiaij.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/aij/mpi/mpicusparse/mpiaijcusparse.cu.html#MatZeroEntries_MPIAIJCUSPARSE">MatZeroEntries_MPIAIJCUSPARSE in src/mat/impls/aij/mpi/mpicusparse/mpiaijcusparse.cu</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/aij/mpi/mpihipsparse/mpiaijhipsparse.hip.c.html#MatZeroEntries_MPIAIJHIPSPARSE">MatZeroEntries_MPIAIJHIPSPARSE in src/mat/impls/aij/mpi/mpihipsparse/mpiaijhipsparse.hip.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/aij/seq/aij.c.html#MatZeroEntries_SeqAIJ">MatZeroEntries_SeqAIJ in src/mat/impls/aij/seq/aij.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/aij/seq/kokkos/aijkok.kokkos.cxx.html#MatZeroEntries_SeqAIJKokkos">MatZeroEntries_SeqAIJKokkos in src/mat/impls/aij/seq/kokkos/aijkok.kokkos.cxx</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/aij/seq/seqcusparse/aijcusparse.cu.html#MatZeroEntries_SeqAIJCUSPARSE">MatZeroEntries_SeqAIJCUSPARSE in src/mat/impls/aij/seq/seqcusparse/aijcusparse.cu</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/aij/seq/seqhipsparse/aijhipsparse.hip.c.html#MatZeroEntries_SeqAIJHIPSPARSE">MatZeroEntries_SeqAIJHIPSPARSE in src/mat/impls/aij/seq/seqhipsparse/aijhipsparse.hip.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/baij/mpi/mpibaij.c.html#MatZeroEntries_MPIBAIJ">MatZeroEntries_MPIBAIJ in src/mat/impls/baij/mpi/mpibaij.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/baij/seq/baij2.c.html#MatZeroEntries_SeqBAIJ">MatZeroEntries_SeqBAIJ in src/mat/impls/baij/seq/baij2.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/cdiagonal/cdiagonal.c.html#MatZeroEntries_ConstantDiagonal">MatZeroEntries_ConstantDiagonal in src/mat/impls/cdiagonal/cdiagonal.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/dense/mpi/mpidense.c.html#MatZeroEntries_MPIDense">MatZeroEntries_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#MatZeroEntries_SeqDense">MatZeroEntries_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#MatZeroEntries_Elemental">MatZeroEntries_Elemental in src/mat/impls/elemental/matelem.cxx</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/h2opus/cuda/math2opus.cu.html#MatZeroEntries_H2OPUS">MatZeroEntries_H2OPUS in src/mat/impls/h2opus/cuda/math2opus.cu</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/hypre/mhypre.c.html#MatZeroEntries_HYPRE">MatZeroEntries_HYPRE in src/mat/impls/hypre/mhypre.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/is/matis.c.html#MatZeroEntries_IS">MatZeroEntries_IS in src/mat/impls/is/matis.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/nest/matnest.c.html#MatZeroEntries_Nest">MatZeroEntries_Nest in src/mat/impls/nest/matnest.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/sbaij/mpi/mpisbaij.c.html#MatZeroEntries_MPISBAIJ">MatZeroEntries_MPISBAIJ in src/mat/impls/sbaij/mpi/mpisbaij.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/sbaij/seq/sbaij2.c.html#MatZeroEntries_SeqSBAIJ">MatZeroEntries_SeqSBAIJ in src/mat/impls/sbaij/seq/sbaij2.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/scalapack/matscalapack.c.html#MatZeroEntries_ScaLAPACK">MatZeroEntries_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#MatZeroEntries_MPISELL">MatZeroEntries_MPISELL in src/mat/impls/sell/mpi/mpisell.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/sell/seq/sell.c.html#MatZeroEntries_SeqSELL">MatZeroEntries_SeqSELL in src/mat/impls/sell/seq/sell.c</A><BR>


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