PetscSFReduceBegin#

begin reduction (communication) of leafdata into rootdata, to be completed with call to PetscSFReduceEnd()

Synopsis#

#include "petscsf.h" 
PetscErrorCode PetscSFReduceBegin(PetscSF sf, MPI_Datatype unit, const void *leafdata, void *rootdata, MPI_Op op)

Collective

Input Parameters#

sf - star forest
unit - data type
leafdata - values to reduce (communicate)
op - reduction operation

Output Parameter#

rootdata - result of reduction of values (leafdata) from all leaves to each root

Note#

When PETSc is configured with device support, it will use PetscGetMemType() to determine whether the given data pointers are host pointers or device pointers, which may incur a noticeable cost. If you already knew the memory type, you should use PetscSFReduceWithMemTypeBegin() instead.