# ISGetBlockSize
Returns the number of elements in a block. 
## Synopsis
```
#include "petscis.h" 
PetscErrorCode ISGetBlockSize(IS is, PetscInt *size)
```
Not Collective


## Input Parameter

- ***is -*** the index set



## Output Parameter

- ***size -*** the number of elements in a block





## Notes
This is much like the block size for Vecs. 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 IS, not others.


## See Also
 `ISBlockGetSize()`, `ISGetSize()`, `ISCreateBlock()`, `ISSetBlockSize()`

## Level
intermediate

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

## Examples
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/vec/is/is/tutorials/ex3.c.html">src/vec/is/is/tutorials/ex3.c.html</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/vec/is/is/tutorials/ex3f90.F90.html">src/vec/is/is/tutorials/ex3f90.F90.html</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](/docs/manualpages/index.md)  
[Index of all manual pages](/docs/manualpages/singleindex.md)  
