Retrieving the Partition

After balancing the graph the resulting assignment of graph vertices to processors can be retrieved using the following call:

  // C++
  agi::PartitionMap* map = g->getPartition();

In C++, the returned PartitionMap maps from the vertex global ids to the communicator rank that they should be assigned. Every vertex that originally belonged on a part before partitioning will have an entry in the map.

The PartitionMap structure supports two methods of access. The first provides an iterator to access the pairs of vertex global id to part info. This works well for application data that supports random access via global id.

  agi::PartitionMap::iterator itr;
  for (itr=map->begin();itr!=map->end();itr++) {
    agi::gid_t gid = itr->first;
    int new_owner = itr->second;
    ...
  }

The second method supports random access to the part assignment given the global id.

  for(each data representing Ngraph vertices) {
    //get gid of the data entry
    int new_owner = map->at(data);
    ...
  }

In FORTRAN,

  // FORTRAN
  call cengpar_getPartition(graph, verts, parts, nverts)

returns the list of global vertex ids, verts, their new process assignment, parts, and the size of these two arrays, nverts, which is equal to the number of owned vertices on the calling process.