SYNTAX

   C Syntax
          #include <mpi.h>

          int MPI_Init(int *argc, char ***argv)

   Fortran Syntax
          USE MPI
          ! or the older form: INCLUDE 'mpif.h'
          MPI_INIT(IERROR)
               INTEGER IERROR

   Fortran 2008 Syntax
          USE mpi_f08
          MPI_Init(ierror)
               INTEGER, OPTIONAL, INTENT(OUT) :: ierror

INPUT PARAMETERS

       • argc: C only: Pointer to the number of arguments.

       • argv: C only: Argument vector.

OUTPUT PARAMETER

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

DESCRIPTION

       This  routine,  or MPI_Init_thread, must be called before most other MPI routines are called. There are a
       small number of errors, such as MPI_Initialized and MPI_Finalized. MPI can be initialized at  most  once;
       subsequent calls to MPI_Init or MPI_Init_thread are erroneous.

       All  MPI  programs  must  contain a call to MPI_Init or MPI_Init_thread.  Open MPI accepts the C argc and
       argv arguments to main, but neither modifies, interprets, nor distributes them:

          /* declare variables */
          MPI_Init(&argc, &argv);
          /* parse arguments */
          /* main program */
          MPI_Finalize();

NOTES

       The Fortran version does not have provisions for argc and argv and takes only IERROR.

       The MPI Standard does not say what a program can do before an MPI_Init or after an MPI_Finalize.  In  the
       Open  MPI  implementation, it should do as little as possible. In particular, avoid anything that changes
       the external state of the program, such as opening files, reading standard input, or writing to  standard
       output.

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_thread,  after
       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 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_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 was called on that communicator. If called on a
         window or file, acts as if 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 then MPI_Comm_set_errhandler

       • MPI_File_create_errhandler then MPI_File_set_errhandler

       • MPI_Session_create_errhandler then MPI_Session_set_errhandler or at MPI_Session_init

       • MPI_Win_create_errhandler then MPI_Win_set_errhandler

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

       See the MPI man page for a full list of MPI error codes.

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

       SEE ALSO:

          • MPI_Init_thread

          • MPI_Initialized

          • MPI_Finalize

          • MPI_Finalized

COPYRIGHT

       2003-2025, The Open MPI Community

                                                  Feb 17, 2025                                       MPI_INIT(3)