In this lesson we have encountered several new operations: group and communicator manipulation functions, and the all-reduce function:
MPI_Comm_group extracts a group associated with a
communicator; discussed in section 6.4.1
MPI_Group_excl creates a new group by exluding named
processes from a given group; discussed in section 6.4.1
MPI_Comm_create creates a new communicator associated
with a given group; discussed in section 6.4.1
MPI_Group_free releases the name associated with
a given group; the group itself may survive inside a communicator
if such was associated with it before; discussed in section
6.4.1
MPI_Comm_free releases a communicator; discussed in section
6.4.3
MPI_Allreduce performs a reduction operation on data
contributed by participating processes and delivers the result to each
process; discussed in section 6.4.3