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# PetscParallelSortInt
Globally sort a distributed array of integers 
## Synopsis
```
#include "petscis.h" 
PetscErrorCode PetscParallelSortInt(PetscLayout mapin, PetscLayout mapout, PetscInt keysin[], PetscInt keysout[])
```
Collective


## Input Parameters

- ***mapin -*** `PetscLayout` describing the distribution of the input keys
- ***mapout -*** `PetscLayout` describing the desired distribution of the output keys
- ***keysin -*** the pre-sorted array of integers



## Output Parameter

- ***keysout -*** the array in which the sorted integers will be stored.  If mapin == mapout, then keysin may be equal to keysout.





## Notes

## This implements a distributed samplesort, which, with local array sizes n_in and n_out, global size N, and global number of processes P, does
```none
  - sorts locally
  - chooses pivots by sorting (in parallel) (P-1) pivot suggestions from each process using bitonic sort and allgathering a subset of (P-1) of those
  - using to the pivots to repartition the keys by all-to-all exchange
  - sorting the repartitioned keys locally (the array is now globally sorted, but does not match the mapout layout)
  - redistributing to match the mapout layout
```


If keysin != keysout, then keysin will not be changed during `PetscParallelSortInt()`.


## See Also
 `PetscSortInt()`, `PetscParallelSortedInt()`

## Level
developer

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/vec/is/utils/psort.c.html#PetscParallelSortInt">src/vec/is/utils/psort.c</A>


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


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