petsc-3.12.1 2019-10-22
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# PetscSFPattern

Pattern of the PetscSF graph

### Synopsis

    typedef enum {PETSCSF_PATTERN_GENERAL=0,PETSCSF_PATTERN_ALLGATHER,PETSCSF_PATTERN_GATHER,PETSCSF_PATTERN_ALLTOALL} PetscSFPattern;

     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/v). One sets the graph with PetscSFSetGraphWithPattern().

     PETSCSF_PATTERN_GATHER    - A graph that rank 0 gathers all roots from all ranks (like MPI_Gather/v 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

PetscSFSetGraph(), PetscSFSetGraphWithPattern()

### Level

beginner

### Location

src/vec/is/sf/../../../../include/petscsf.h
Index of all PetscSF routines
Table of Contents for all manual pages
Index of all manual pages