Collective communication calls enable a programmer to give commands to a subgroup o fthe processors in the virtual machine. Members of a subgroup are identified by their communicator, and a processor may be a member of more than one subgroup. Collective communication calls make it easier to perform tasks such as process synchronization, global summation, scattering and gathering data.
Here the MPI_BARRIER, MPI_BCAST and MPI_REDUCE
calls will be detailed. Other useful collective communication calls
include MPI_SCATTER, MPI_GATHER, MPI_REDUCE,
MPI_ALLREDUCE, MPI_SCAN.