mpi.comm.get.parent is mainly used by slaves to find the
intercommunicator or the parent who spawns them. The intercommunicator is saved
in the specified comm number.
mpi.comm.remote.size is mainly used by master to find the total number of
slaves spawned.
mpi.comm.test.inter tests if a comm is an intercomm or not.
mpi.comm.get.parent(comm = 2)
mpi.comm.remote.size(comm = 2)
mpi.comm.test.inter(comm = 2)an intercommunicator number.
mpi.comm.get.parent and mpi.comm.test.inter return 1 if success
and 0 otherwise.
mpi.comm.remote.size returns the total number of members in the remote
group in an intercomm.