:orphan:
# PetscSFPattern
Pattern of the `PetscSF` graph 
## Synopsis
```
typedef enum {
  PETSCSF_PATTERN_GENERAL = 0,
  PETSCSF_PATTERN_ALLGATHER,
  PETSCSF_PATTERN_GATHER,
  PETSCSF_PATTERN_ALLTOALL
} PetscSFPattern;
```

## Values

- ***`PETSCSF_PATTERN_GENERAL`   -*** A general graph. One sets the graph with `PetscSFSetGraph()` and usually does not use this enum directly.
- ***`PETSCSF_PATTERN_ALLGATHER` -*** A graph that every rank gathers all roots from all ranks (like `MPI_Allgather()`). One sets the graph with `PetscSFSetGraphWithPattern()`.
- ***`PETSCSF_PATTERN_GATHER`    -*** A graph that rank 0 gathers all roots from all ranks (like `MPI_Gatherv()` with root=0). One sets the graph with `PetscSFSetGraphWithPattern()`.
- ***`PETSCSF_PATTERN_ALLTOALL`  -*** A graph that every rank gathers different roots from all ranks (like `MPI_Alltoall()`). One sets the graph with `PetscSFSetGraphWithPattern()`.
In an ALLTOALL graph, we assume each process has <size> leaves and <size> roots, with each leaf connecting to a remote root. Here <size> is
the size of the communicator. This does not mean one can not communicate multiple data items between a pair of processes. One just needs to
create a new MPI datatype for the multiple data items, e.g., by `MPI_Type_contiguous`.




## See Also
 `PetscSF`, `PetscSFSetGraph()`, `PetscSFSetGraphWithPattern()`

## Level
beginner

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/include/petscsf.h.html#PetscSFPattern">include/petscsf.h</A>


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