90. Broadcast

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MPI_BCAST( buffer, count, datatype, root, comm )
INOUT bufferstarting address of buffer (choice)
IN count number of entries in buffer (non-negative integer)
IN datatype data type of buffer (handle)
IN root rank of broadcast root (integer)
IN comm communicator (handle)

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

<type> BUFFER(*)
void MPI::Comm::Bcast(void* buffer, int count, const MPI::Datatype& datatype, int root) const = 0

If comm is an intracommunicator, MPI_BCAST broadcasts a message from the process with rank root to all processes of the group, itself included. It is called by all members of the group using the same arguments for comm and root. On return, the content of root's buffer is copied to all other processes. General, derived datatypes are allowed for datatype. The type signature of count, datatype on any process must be equal to the type signature of count, datatype at the root. This implies that the amount of data sent must be equal to the amount received, pairwise between each process and the root. MPI_BCAST and all other data-movement collective routines make this restriction. Distinct type maps between sender and receiver are still allowed. The ``in place'' option is not meaningful here.

If comm is an intercommunicator, then the call involves all processes in the intercommunicator, but with one group (group A) defining the root process. All processes in the other group (group B) pass the same value in argument root, which is the rank of the root in group A. The root passes the value MPI_ROOT in root. All other processes in group A pass the value MPI_PROC_NULL in root. Data is broadcast from the root to all processes in group B. The buffer arguments of the processes in group B must be consistent with the buffer argument of the root.

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