petsc-3.14.5 2021-03-03
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# PetscSFCompose

Compose a new PetscSF by putting the second SF under the first one in a top (roots) down (leaves) view

### Synopsis

    #include "petscsf.h"
    PetscErrorCode PetscSFCompose(PetscSF sfA,PetscSF sfB,PetscSF *sfBA)

### Input Parameters

| sfA | - The first PetscSF
| sfB | - The second PetscSF

### Output Parameters

| sfBA | - The composite SF

### Notes

Currently, the two SFs must be defined on congruent communicators and they must be true star forests, i.e. the same leaf is not connected with different roots.

sfA's leaf space and sfB's root space might be partially overlapped. The composition builds a graph with sfA's roots and sfB's leaves only when there is a path between them. Unconnected nodes (roots or leaves) are not in sfBA. Doing a Bcast on the new SF is equivalent to doing a Bcast on sfA, then a Bcast on sfB, on connected nodes.

### See Also

PetscSF, PetscSFComposeInverse(), PetscSFGetGraph(), PetscSFSetGraph()

### Level

developer

### Location

src/vec/is/sf/interface/sf.c
Index of all PetscSF routines
Table of Contents for all manual pages
Index of all manual pages