Indicates that this process is the root for a collective operation. The root process should
pass this constant in as the value for root for calls to collective operations.
Other processes in the same group as root should use Null. Processes
in the group sending to the root should use the root process' local rank.
Namespace:
MPIAssembly: MPI (in MPI.dll)
Version: 1.0.0.0 (1.0.0.0)