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NAME

MPI_Bcast - Broadcast a buffer to all members of a communicator

SYNOPSIS

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

#include <pmpi.h> int PMPI_Bcast(void *buf , int count , MPI_Datatype datatype , int root , MPI_Comm comm );

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

INCLUDE 'mpif.h' MPI_BCAST(buf , count , datatype , root , comm , ierr ) <type> buf (*) INTEGER count , datatype , root , comm , ierr

INPUT PARAMETERS

buf - buffer (array)

count - count of elements in buffer (integer)

datatype - type of elements in buffer (handle)

root - root rank (integer)

comm - communicator for messages (handle)

OUTPUT PARAMETER

buf - buffer (array)

DESCRIPTION

The MPI_Bcast() function is used to send messages from the process with rank root in the communicator comm , to all other processes in the communicator. The sends may (or may not) block depending on the amount of internal buffering done in the MPI implementation. Every other process in the communicator will wait until the broadcasted message is received. The sends (and receives) consist of count elements of type datatype from or into an array specified by buf . Each process will receive a duplicate message.

The communicator must be a valid one (not MPI_COMM_NULL). Similarly, root must be valid. (not MPI_PROC_NULL). PMPI_Bcast() is the profiling version of this function.

ERRORS

All MPI routines except for MPI_Wtime and MPI_Wtick return an error code. The the current MPI error handler is invoked if the return value is not MPI_SUCCESS. The default error handler aborts, but this may be changed with by using the MPI_Errhandler_set() function. The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned instead. Note that MPI does not guarentee that an MPI program can continue past an error. In this implementation, all errors except MPI_ERR_INTERN or MPI_ERR_OTHER should always be recoverable.

In C, the error code is passed as the return value. In FORTRAN, all functions have an parameter ierr which returns the error code. MPI C++ functions do not directly return an error code. However, C++ users may want to use the MPI::ERRORS_THROW_EXCEPTIONS handler. This will throw an MPI::Exception with the corresponding error code. To prevent exceptions from being raised from within C and Fortran code, they will see all error return values as MPI_ERR_PENDING when this handler is chosen. In this implementation, call MPI::throw_exception() to throw the correct exception if this occurs.

MPI_SUCCESS - No error;

MPI_ERR_PENDING - Pending exception;

MPI_ERR_COMM - Invalid communicator;

MPI_ERR_COUNT - Invalid element count;

MPI_ERR_BUFFER - Invalid buffer;

MPI_ERR_TYPE - Invalid data type;

MPI_ERR_ROOT - Invalid root;

MPI_ERR_INTERN - Out of memory error.

SEE ALSO

MPI_Send (3) MPI_Recv (3) MPI_Barrier (3) MPI_Scatter (3) MPI_Gather (3) MPI_Alltoall (3)

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