trusty (3) MPI_Bcast.openmpi.3.gz

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 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.

       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 appropriate 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++ functions 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.