:orphan:
# ISSetBlockSize
informs an index set that it has a given block size 
## Synopsis
```
#include "petscis.h" 
PetscErrorCode ISSetBlockSize(IS is, PetscInt bs)
```
Logicall Collective


## Input Parameters

- ***is -*** index set
- ***bs -*** block size





## Notes
This is much like the block size for `Vec`s. It indicates that one can think of the indices as
being in a collection of equal size blocks. For `ISBLOCK` these collections of blocks are all contiquous
within a block but this is not the case for other `IS`.

`ISBlockGetIndices()` only works for `ISBLOCK`, not others.


## See Also
 `IS`, `ISGetBlockSize()`, `ISCreateBlock()`, `ISBlockGetIndices()`,

## Level
intermediate

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/vec/is/is/interface/index.c.html#ISSetBlockSize">src/vec/is/is/interface/index.c</A>

## Examples
<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/ex73.c.html">src/ksp/ksp/tutorials/ex73.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex76.c.html">src/ksp/ksp/tutorials/ex76.c</A><BR>

## Implementations

<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/vec/is/is/impls/block/block.c.html#ISSetBlockSize_Block">ISSetBlockSize_Block in src/vec/is/is/impls/block/block.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/vec/is/is/impls/general/general.c.html#ISSetBlockSize_General">ISSetBlockSize_General in src/vec/is/is/impls/general/general.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/vec/is/is/impls/stride/stride.c.html#ISSetBlockSize_Stride">ISSetBlockSize_Stride in src/vec/is/is/impls/stride/stride.c</A><BR>


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[Edit on GitLab](https://gitlab.com/petsc/petsc/-/edit/release/src/vec/is/is/interface/index.c)


[Index of all IS routines](index.md)  
[Table of Contents for all manual pages](/manualpages/index.md)  
[Index of all manual pages](/manualpages/singleindex.md)