.\" -*- nroff -*-
.\" Copyright (c) 2010-2015 Cisco Systems, Inc.  All rights reserved.
.\" Copyright 2006-2008 Sun Microsystems, Inc.
.\" Copyright (c) 1996 Thinking Machines Corporation
.\" $COPYRIGHT$
.TH MPI_Init 3 "Sep 30, 2023" "4.1.6" "Open MPI"

.SH NAME
\fBMPI_Init\fP \- Initializes the MPI execution environment

.SH SYNTAX
.ft R

.SH C Syntax
.nf
#include <mpi.h>
int MPI_Init(int *\fIargc\fP, char ***\fIargv\fP)

.fi
.SH Fortran Syntax
.nf
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_INIT(\fIIERROR\fP)
	INTEGER	\fIIERROR\fP

.fi
.SH Fortran 2008 Syntax
.nf
USE mpi_f08
MPI_Init(\fIierror\fP)
	INTEGER, OPTIONAL, INTENT(OUT) :: \fIierror\fP

.fi
.SH C++ Syntax
.nf
#include <mpi.h>
void MPI::Init(int& \fIargc\fP, char**& \fIargv\fP)
void MPI::Init()

.fi
.SH INPUT PARAMETERS
.ft R
.TP 1i
argc
C/C++ only: Pointer to the number of arguments.
.TP 1i
argv
C/C++ only: Argument vector.

.SH OUTPUT PARAMETER
.ft R
.TP 1i
IERROR
Fortran only: Error status (integer).

.SH DESCRIPTION
.ft R
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.
.sp
All MPI programs must contain a call to MPI_Init or
MPI_Init_thread. Open MPI accepts the C/C++ \fIargc\fP and \fIargv\fP
arguments to main, but neither modifies, interprets, nor distributes
them:
.sp
.nf
	{
		/* declare variables */
		MPI_Init(&argc, &argv);
		/* parse arguments */
		/* main program */
		MPI_Finalize();
	}
.fi

.SH NOTES
.ft R
The Fortran version does not have provisions for \fIargc\fP and
\fIargv\fP and takes only IERROR.
.sp
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.

.SH ERRORS
.ft R
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.
.sp
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.
.sp
See the MPI man page for a full list of MPI error codes.

.SH SEE ALSO
.ft R
.nf
MPI_Init_thread
MPI_Initialized
MPI_Finalize
MPI_Finalized