Broadcasts a message from the process with rank "root" to all other processes of the group.


#include "mpi.h"
int MPI_Bcast ( void *buffer, int count, MPI_Datatype datatype, int root, 
               MPI_Comm comm )

Input/output Parameters

buffer starting address of buffer (choice)
count number of entries in buffer (integer)
datatype data type of buffer (handle)
root rank of broadcast root (integer)
comm communicator (handle)


If the underlying device does not take responsibility, this function uses a tree-like algorithm to broadcast the message to blocks of processes. A linear algorithm is then used to broadcast the message from the first process in a block to all other processes. MPIR_BCAST_BLOCK_SIZE determines the size of blocks. If this is set to 1, then this function is equivalent to using a pure tree algorithm. If it is set to the size of the group or greater, it is a pure linear algorithm. The value should be adjusted to determine the most efficient value on different machines.

Notes for Fortran

All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK) have an additional argument ierr at the end of the argument list. ierr is an integer and has the same meaning as the return value of the routine in C. In Fortran, MPI routines are subroutines, and are invoked with the call statement.

All MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGER in Fortran.


All MPI routines (except MPI_Wtime and MPI_Wtick) return an error value; C routines as the value of the function and Fortran routines in the last argument. Before the value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job. The error handler may be changed with MPI_Errhandler_set; the predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarentee that an MPI program can continue past an error.

No error; MPI routine completed successfully.
Invalid communicator. A common error is to use a null communicator in a call (not even allowed in MPI_Comm_rank).
Invalid count argument. Count arguments must be non-negative; a count of zero is often valid.
Invalid datatype argument. May be an uncommitted MPI_Datatype (see MPI_Type_commit).
Invalid buffer pointer. Usually a null buffer where one is not valid.
Invalid root. The root must be specified as a rank in the communicator. Ranks must be between zero and the size of the communicator minus one.