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# MATIS
MATIS = "is" - A matrix type to be used for using the non-overlapping domain decomposition methods (e.g. `PCBDDC` or `KSPFETIDP`). This stores the matrices in globally unassembled form. Each processor assembles only its local Neumann problem and the parallel matrix vector product is handled "implicitly". 
## Options Database Keys

- ***-mat_type is -*** sets the matrix type to `MATIS`.
- ***-matis_fixempty -*** Fixes local matrices in case of empty local rows/columns.
- ***-matis_storel2l -*** stores the local-to-local operators generated by the Galerkin process of `MatPtAP()`.





## Notes
Options prefix for the inner matrix are given by `-is_mat_xxx`

You must call `MatSetLocalToGlobalMapping()` before using this matrix type.

You can do matrix preallocation on the local matrix after you obtain it with
`MatISGetLocalMat()`; otherwise, you could use `MatISSetPreallocation()`


## See Also
 [](ch_matrices), `Mat`, `MATIS`, `Mat`, `MatISGetLocalMat()`, `MatSetLocalToGlobalMapping()`, `MatISSetPreallocation()`, `MatCreateIS()`, `PCBDDC`, `KSPFETIDP`

## Level
advanced

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/mat/impls/is/matis.c.html#MATIS">src/mat/impls/is/matis.c</A>

## Examples
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex29.c.html">src/ksp/ksp/tutorials/ex29.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex34.c.html">src/ksp/ksp/tutorials/ex34.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex71.c.html">src/ksp/ksp/tutorials/ex71.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex72.c.html">src/ksp/ksp/tutorials/ex72.c</A><BR>


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