Communicators
- A key concept used throughout MPI is that of the communication domain.
- A communication domain is a set of processes that are allowed to communicate with each other.
- Information about communication domains is stored in variables of type MPI_Comm, that are called communicators.
- These communicators are used as arguments to all message transfer MPI routines.
- They uniquely identify the processes participating in the message transfer operation.
- In general, all the processes may need to communicate with each other.
- For this reason, MPI defines a default communicator called MPI_COMM_WORLD which includes all the processes involved.