The master process for a client is the process of lowest rank running under the client. Note that process rank 0 within a communicator is always a master process. Then the master processes are ranks 0,2 and 6 and they are numbered 0,1 and 2 respectively. The descriptions of the IMPI collectives make use of the following utility functions. Each implementation is free to implement them in whatever manner they see fit.
Returns TRUE iff process rank r in comm is a master process.
Returns TRUE iff processes ranked r1 and r2 in comm are local to one-another. If process rank r in comm is a master process returns its master number else returns -1. Returns the master number of the master process local to process rank r in comm. Returns the number of master processes in comm. Returns the number of processes in comm local to process rank r in comm.