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# VecWhichEqual
Creates an index set containing the indices where the vectors `Vec1` and `Vec2` have identical elements. 
## Synopsis
```
#include "petscvec.h"  
PetscErrorCode VecWhichEqual(Vec Vec1, Vec Vec2, IS *S)
```
Collective


## Input Parameters

- ***Vec1 -*** the first vector to compare
- ***Vec2 -*** the second two vector to compare



## OutputParameter

- ***S -*** The index set containing the indices i where vec1[i] == vec2[i]





## Note
The two vectors must have the same parallel layout


## See Also
 `Vec`

## Level
advanced

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/vec/vec/utils/projection.c.html#VecWhichEqual">src/vec/vec/utils/projection.c</A>


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


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