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()). 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 leaves and roots, with each leaf connecting to a remote root. Here 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.

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