In many cases, one process needs to send (broadcast) some data (either a scalar or vector) to all the processes in a group. MPI provides the broadcast primitive MPI_BCAST to accomplish this task. The syntax of the MPI_BCAST is given by:

C

int MPI_Bcast

(void* buffer, int count, MPI_Datatype datatype, int root, MPI_Comm comm)

FORTRAN

MPI_BCAST

(buffer, count, datatype, root, comm, ierr)

where:

buffer	is the starting address of a buffer,
count	is an integer indicating the number of data elements in the buffer,
datatype	is MPI defined constant indicating the data type of the elements in the buffer,
root	is an integer indicating the rank of broadcast root process, and
comm	is the communicator.

The MPI_BCAST must be called by each node in the group, specifying the same comm and root. The message is sent from the root process to all processes in the group, including the root process.

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Example:

• "hello, world" example used in earlier modules could use broadcast instead of multiple sends and receives

use MPI
character(12) message 
integer rank,root
data root/0/ 
call MPI_INIT(ierr)
call MPI_COMM_RANK(MPI_COMM_WORLD, rank, ierr) 
if (rank .eq. root) then 
    message = 'Hello, world'
endif 
call MPI_BCAST(message, 12, MPI_CHARACTER, root, &
         MPI_COMM_WORLD, ierr) 
print*, 'node', rank, ':', message 
call MPI_FINALIZE(ierr)
end