# PCFieldSplitRestrictIS
Restricts the fieldsplit `IS`s to be within a given `IS`. 
## Synopsis
```
#include "petscpc.h" 
PetscErrorCode PCFieldSplitRestrictIS(PC pc, IS isy)
```

## Input Parameters

- ***pc  -*** the preconditioner context
- ***is -*** the index set that defines the indices to which the fieldsplit is to be restricted





## Developer Note
It seems the resulting `IS`s will not cover the entire space, so
how can they define a convergent preconditioner? Needs explaining.


## See Also
 [](sec_block_matrices), `PCFIELDSPLIT`, `PCFieldSplitSetFields()`, `PCFieldSplitSetIS()`

## Level
advanced

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

## Implementations

<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/pc/impls/fieldsplit/fieldsplit.c.html#PCFieldSplitRestrictIS_FieldSplit">PCFieldSplitRestrictIS_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)


[Index of all PC routines](index.md)  
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