MPI_BCAST, MPI_Bcast

Purpose

Broadcasts a message from root to all tasks in comm.

C synopsis

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

C++ synopsis

#include mpi.h
void MPI::Comm::Bcast(void* buffer, int count, const MPI::Datatype& datatype,
                      int root) const;

FORTRAN synopsis

include 'mpif.h' or use mpi
MPI_BCAST(CHOICE BUFFER,INTEGER COUNT,INTEGER DATATYPE,INTEGER ROOT,
          INTEGER COMM,INTEGER IERROR)

Description

This subroutine broadcasts a message from root to all tasks in comm. The
contents of root's communication buffer are copied to all tasks on return.

The type signature of count, datatype on any task must be equal to the type
signature of count, datatype at the root. This means the amount of data
sent must be equal to the amount of data received, pair wise between each
task and the root. Distinct type maps between sender and receiver are
allowed.

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

When you use this subroutine in a threads application, make sure all
collective operations on a particular communicator occur in the same order
at each task. See IBM Parallel Environment for AIX: MPI Programming Guide
for more information on programming with MPI in a threads environment.

Parameters

buffer
     is the starting address of the buffer (choice) (INOUT)
count
     is the number of elements in the buffer (integer) (IN)
datatype
     is the datatype of the buffer elements (handle) (IN)
root
     is the rank of the root task (integer) (IN)
comm
     is the communicator (handle) (IN)
IERROR
     is the FORTRAN return code. It is always the last argument.

Notes

In the 64-bit library, this function uses a shared memory optimization
among the tasks on a node. This optimization is discussed in the chapter
"Using shared memory" of IBM Parallel Environment for AIX: MPI Programming
Guide, and is enabled by default. This optimization is not available to
32-bit programs.

Errors

Fatal errors:

Invalid communicator

Invalid count
     count < 0

Invalid datatype

Type not committed

Invalid root

     For an intracommunicator: root < 0 or root >= groupsize

     For an intercommunicator: root < 0 and is neither MPI_ROOT nor
     MPI_PROC_NULL, or root >= groupsize of the remote group

Unequal message lengths

Invalid use of MPI_IN_PLACE

MPI not initialized

MPI already finalized

Develop mode error if:

Inconsistent root

Inconsistent message length

Related information

     MPE_IBCAST