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# PCFieldSplitSetIS
Sets the exact elements for a split in a `PCFIELDSPLIT` 
## Synopsis
```
#include "petscpc.h" 
PetscErrorCode PCFieldSplitSetIS(PC pc, const char splitname[], IS is)
```
Logically Collective


## Input Parameters

- ***pc  -*** the preconditioner context
- ***splitname -*** name of this split, if `NULL` the number of the split is used
- ***is -*** the index set that defines the elements in this split





## Notes
Use `PCFieldSplitSetFields()`, for splits defined by strided types.

This function is called once per split (it creates a new split each time).  Solve options
for this split will be available under the prefix -fieldsplit_SPLITNAME_.


## See Also
 [](sec_block_matrices), `PC`, `PCFieldSplitGetSubKSP()`, `PCFIELDSPLIT`, `PCFieldSplitSetBlockSize()`

## Level
intermediate

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/pc/impls/fieldsplit/fieldsplit.c.html#PCFieldSplitSetIS">src/ksp/pc/impls/fieldsplit/fieldsplit.c</A>

## Examples
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex81.c.html">src/ksp/ksp/tutorials/ex81.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/snes/tutorials/ex28.c.html">src/snes/tutorials/ex28.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/snes/tutorials/ex70.c.html">src/snes/tutorials/ex70.c</A><BR>

## Implementations

<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/pc/impls/fieldsplit/fieldsplit.c.html#PCFieldSplitSetIS_FieldSplit">PCFieldSplitSetIS_FieldSplit in src/ksp/pc/impls/fieldsplit/fieldsplit.c</A><BR>


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[Edit on GitLab](https://gitlab.com/petsc/petsc/-/edit/release/src/ksp/pc/impls/fieldsplit/fieldsplit.c)


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