NAME

       MPI_Init - Initializes the MPI execution environment

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

C++ Syntax

       #include <mpi.h>
       void MPI::Init(int& argc, char**& argv)
       void MPI::Init()

INPUT PARAMETERS

       argc      C/C++ only: Pointer to the number of arguments.

       argv      C/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 exceptions, 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/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 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.

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

SEE ALSO

       MPI_Init_thread
       MPI_Initialized
       MPI_Finalize
       MPI_Finalized

4.1.6                                             Sep 30, 2023                                       MPI_Init(3)