MPI_Bcast(3OpenMPI) MPI_Bcast(3OpenMPI)
NAME
MPI_Bcast - Broadcasts a message from the process with rank root to all other processes of the group.
SYNTAX
C Syntax
#include <mpi.h>
int MPI_Bcast(void *buffer, int count, MPI_Datatype datatype,
int root, MPI_Comm comm)
Fortran Syntax
INCLUDE 'mpif.h'
MPI_BCAST(BUFFER, COUNT, DATATYPE, ROOT, COMM, IERROR)
<type> BUFFER(*)
INTEGER COUNT, DATATYPE, ROOT, COMM, IERROR
C++ Syntax
#include <mpi.h>
void MPI::Comm::Bcast(void* buffer, int count,
const MPI::Datatype& datatype, int root) const = 0
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).
OUTPUT PARAMETER
IERROR Fortran only: Error status (integer).
DESCRIPTION
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 group using the same arguments for comm, root. On return, the contents of root's communication buffer has been copied to all processes.
General, derived datatypes are allowed for datatype. The type signature of count, datatype on any process must be equal to the type signa-
ture 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.
Example: Broadcast 100 ints from process 0 to every process in the group.
MPI_Comm comm;
int array[100];
int root=0;
...
MPI_Bcast( array, 100, MPI_INT, root, comm);
As in many of our sample code fragments, we assume that some of the variables (such as comm in the example above) have been assigned appro-
priate values.
WHEN COMMUNICATOR IS AN INTER-COMMUNICATOR
When the communicator is an inter-communicator, the root process in the first group broadcasts data to all the processes in the second
group. The first group defines the root process. That process uses MPI_ROOT as the value of its root argument. The remaining processes
use MPI_PROC_NULL as the value of their root argument. All processes in the second group use the rank of that root process in the first
group as the value of their root argument. The receive buffer arguments of the processes in the second group must be consistent with the
send buffer argument of the root process in the first group.
NOTES
This function does not support the in-place option.
ERRORS
Almost all MPI routines return an error value; C routines as the value of the function and Fortran routines in the last argument. C++ func-
tions do not return errors. If the default error handler is set to MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism
will be used to throw an MPI:Exception object.
Before the error value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job, except for
I/O function errors. The error handler may be changed with MPI_Comm_set_errhandler; the predefined error handler MPI_ERRORS_RETURN may be
used to cause error values to be returned. Note that MPI does not guarantee that an MPI program can continue past an error.
Open MPI 1.2 September 2006 MPI_Bcast(3OpenMPI)
