MPI_BCAST_INIT(3)				     Open MPI					 MPI_BCAST_INIT(3)

       MPI_Bcast  <#mpi-bcast>, MPI_Ibcast <#mpi-ibcast> - 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)

	  int MPI_Ibcast(void *buffer, int count, MPI_Datatype datatype,
	      int root, MPI_Comm comm, MPI_Request *request)

   Fortran Syntax
	  USE MPI
	  ! or the older form: INCLUDE 'mpif.h'
	  MPI_BCAST(BUFFER, COUNT, DATATYPE, ROOT, COMM, IERROR)
	      <type>  BUFFER(*)
	      INTEGER COUNT, DATATYPE, ROOT, COMM, IERROR

	  MPI_IBCAST(BUFFER, COUNT, DATATYPE, ROOT, COMM, REQUEST, IERROR)
	      <type>  BUFFER(*)
	      INTEGER COUNT, DATATYPE, ROOT, COMM, REQUEST, IERROR

   Fortran 2008 Syntax
	  USE mpi_f08
	  MPI_Bcast(buffer, count, datatype, root, comm, ierror)
	      TYPE(*), DIMENSION(..) :: buffer
	      INTEGER, INTENT(IN) :: count, root
	      TYPE(MPI_Datatype), INTENT(IN) :: datatype
	      TYPE(MPI_Comm), INTENT(IN) :: comm
	      INTEGER, OPTIONAL, INTENT(OUT) :: ierror

	  MPI_Ibcast(buffer, count, datatype, root, comm, request, ierror)
	      TYPE(*), DIMENSION(..), ASYNCHRONOUS :: buffer
	      INTEGER, INTENT(IN) :: count, root
	      TYPE(MPI_Datatype), INTENT(IN) :: datatype
	      TYPE(MPI_Comm), INTENT(IN) :: comm
	      TYPE(MPI_Request), INTENT(OUT) :: request
	      INTEGER, OPTIONAL, INTENT(OUT) :: ierror

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 PARAMETERS
       • request: Request (handle, non-blocking only).

       • ierror: Fortran only: Error status (integer).

DESCRIPTION
       MPI_Bcast <#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 o f 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	<#
       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 return result of the function and Fortran
       routines in the last argument.

       Before the error value is returned, the current MPI error handler associated with the communication  object
       (e.g.,  communicator, window, file) is called.  If no communication object is associated with the MPI call,
       then the call is considered attached to MPI_COMM_SELF and will call the associated MPI error handler.  When
       MPI_COMM_SELF  is  not  initialized  (i.e., before MPI_Init <#mpi-init>/MPI_Init_thread <#mpi-init-thread>,
       after MPI_Finalize <#mpi-finalize>, or when using the Sessions Model  exclusively)  the	error  raises  the
       initial	error  handler.	 The  initial  error  handler can be changed by calling MPI_Comm_set_errhandler <#
       mpi-comm-set-errhandler> on MPI_COMM_SELF when using the World model,  or  the  mpi_initial_errhandler  CLI
       argument	  to   mpiexec	 or   info  key	 to  MPI_Comm_spawn  <#mpi-comm-spawn>/MPI_Comm_spawn_multiple	<#
       mpi-comm-spawn-multiple>.  If no other appropriate error handler has been set, then  the	 MPI_ERRORS_RETURN
       error  handler  is  called  for	MPI I/O functions and the MPI_ERRORS_ABORT error handler is called for all
       other MPI functions.

       Open MPI includes three predefined error handlers that can be used:

       • MPI_ERRORS_ARE_FATAL Causes the program to abort all connected MPI processes.

       • MPI_ERRORS_ABORT An error handler that can be invoked on a communicator, window, file, or  session.  When
	 called on a communicator, it acts as if MPI_Abort <#mpi-abort> was called on that communicator. If called
	 on  a window or file, acts as if MPI_Abort <#mpi-abort> was called on a communicator containing the group
	 of processes in the corresponding window or file. If called on a session, aborts only the local process.

       • MPI_ERRORS_RETURN Returns an error code to the application.

       MPI applications can also implement their own error handlers by calling:

       • MPI_Comm_create_errhandler	<#mpi-comm-create-errhandler>	  then	   MPI_Comm_set_errhandler	<#
	 mpi-comm-set-errhandler>

       • MPI_File_create_errhandler	 <#mpi-file-create-errhandler>	   then	    MPI_File_set_errhandler	<#
	 mpi-file-set-errhandler>

       • MPI_Session_create_errhandler	 <#mpi-session-create-errhandler>   then   MPI_Session_set_errhandler	<#
	 mpi-session-set-errhandler> or at MPI_Session_init <#mpi-session-init>

       • MPI_Win_create_errhandler	<#mpi-win-create-errhandler>	  then	    MPI_Win_set_errhandler	<#
	 mpi-win-set-errhandler>

       Note that MPI does not guarantee that an MPI program can continue past an error.

       See the MPI man page <#open-mpi> for a full list of MPI error codes <#open-mpi-errors>.

       See the Error Handling section of the MPI-3.1 standard for more information.

Copyright
       2003-2026, The Open MPI Community

						   Mar 05, 2026					 MPI_BCAST_INIT(3)
