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MPI_Bcast(3)				     LAM/MPI				     MPI_Bcast(3)

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

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

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

       This function has had the IMPI extensions implemented.  It is legal to call this  function
       on IMPI communicators.

       For  4 or less ranks, a linear algorithm is used, where rank 0 loops over sending the mes-
       sage to each other rank.

       If more than 4 ranks are involved, a tree-based algorithm is used  to  send  the  messages
       from rank 0.

       All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK ) have an additional argu-
       ment 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.

       If an error occurs in an MPI function, the current MPI error handler is called  to  handle
       it.   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 (in C and Fortran; this error handler is less useful in
       with the C++ MPI bindings.   The  predefined  error  handler  MPI::ERRORS_THROW_EXCEPTIONS
       should  be  used in C++ if the error value needs to be recovered).  Note that MPI does not
       guarantee that an MPI program can continue past an error.

       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.  The C++ bindings for
       MPI do not return error values; instead, error values are communicated by throwing  excep-
       tions  of  type	MPI::Exception	(but  not by default).	Exceptions are only thrown if the
       error value is not MPI::SUCCESS

       Note that if the MPI::ERRORS_RETURN handler is set in C++, while MPI functions will return
       upon an error, there will be no way to recover what the actual error value was.
	      - 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 communicator.  LAM/MPI does  not  yet  support	invoking  collectives  on
	      - 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_com-
	      mit ).
	      - 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.

       For more information, please see the official MPI Forum web site, which contains the  text
       of both the MPI-1 and MPI-2 standards.  These documents contain detailed information about
       each MPI function (most of which is not duplicated in these man pages).


       The LAM Team would like the thank the MPICH Team for the handy  program	to  generate  man
       pages  ("doctext"  from ftp://ftp.mcs.anl.gov/pub/sowing/sowing.tar.gz ), the initial for-
       matting, and some initial text for most of the MPI-1 man pages.


LAM/MPI 6.5.8				    11/10/2002				     MPI_Bcast(3)
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