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MPI_Init(3)				     LAM/MPI				      MPI_Init(3)

       MPI_Init -  Initialize the MPI execution environment

       #include <mpi.h>
       int MPI_Init(int *pargc, char ***pargv)

       pargc  - Pointer to the number of arguments
       pargv  - Pointer to the argument vector

       MPI  specifies  no command-line arguments but does allow an MPI implementation to make use
       of them.  LAM/MPI neither uses nor adds any values to the argc and  argv  parameters.   As
       such, it is legal to pass NULL for both argc and argv in LAM/MPI.

       Instead,  LAM/MPI relies upon the mpirun command to pass meta-information between nodes in
       order to start MPI programs (of course, the LAM daemons must have previously been launched
       with  the  lamboot  command).  As such, every rank in MPI_COMM_WORLD will receive the argc
       and argv that was specified with the mpirun command (either via the mpirun command line or
       an app schema) as soon as main begins.  See the mpirun (1) man page for more information.

       If  mpirun  is  not  used  to  start MPI programs, the resulting process will be rank 0 in
       MPI_COMM_WORLD , and MPI_COMM_WORLD will have a size of 1.  This is known as a "singleton"
       MPI.  It should be noted that LAM daemons are still used for singleton MPI programs - lam-
       boot must still have been successfully executed before running a singleton process.

       LAM/MPI takes care to ensure that the normal Unix process model of execution is preserved:
       no  extra  threads or processes are forked from the user's process.  Instead, the LAM dae-
       mons are used for all process management and meta-environment information.   Consequently,
       LAM/MPI	places no restriction on what may be invoked before MPI_Init* or after MPI_Final-
       ize ; this is not a safe assumption for those attempting to write portable MPI programs	-
       see "Portability Concerns", below.

       MPI mandates that the same thread must call MPI_Init or MPI_Init_thread and MPI_Finalize

       Note  that  the	Fortran  binding  for  this  routine has only the error return argument (
       MPI_INIT(ierror) ).

       Because the Fortran and C versions of MPI_Init are different, there is  a  restriction  on
       who can call MPI_Init
	.   The version (Fortran or C) must match the main program.  That is, if the main program
       is in C, then the C version of MPI_Init must be called.	If the main program  is  in  For-
       tran, the Fortran version must be called.

       On  exit  from this routine, all processes will have a copy of the argument list.  This is
       not required by the MPI standard, and truely portable codes should not rely on  it.   This
       is  provided as a service by this implementation (an MPI implementation is allowed to dis-
       tribute the command line arguments but is not required to).

       The LAM implementation of MPI uses, by default, SIGUSR2
	.  This may be changed when LAM is compiled, however, with the --with-signal command line
       switch to LAM's configure script.  Consult your system administrator to see if they speci-
       fied a different signal when LAM was installed.

       LAM/MPI catches several signals for the purpose of printing error messages before invoking
       the  next  signal handler.  That is, LAM "chains" its signal handler to be executed before
       the signal handler that was already set.  This scheme prevents nodes (remote nodes,  espe-
       cially) from silently dying and hanging the remaining MPI ranks because of unfinished com-
       munications - a very confusing situation when debugging parallel programs.

       Therefore, it is safe for users to set their own signal handlers.  If they  wish  the  LAM
       signal  handlers  to be executed as well, users should set their handlers before MPI_Init*
       is invoked.  If users do not wish to have LAM catch signals (a bad idea!), they should set
       their handlers after MPI_Init* is invoked.

       LAM/MPI catches the following signals


       All  other  signals  are  unused by LAM/MPI, and will be passed to their respective signal

       Portable MPI programs cannot assume the same process model that	LAM  uses  (i.e.,  essen-
       tially	the  same  as  POSIX).	 MPI  does  not  mandate  anything  before  MPI_Init  (or
       MPI_Init_thread ), nor anything after MPI_Finalize executes.   Different  MPI  implementa-
       tions  make  different assumptions; some fork auxillary threads and/or processes to "help"
       with the MPI run-time environment (this may interfere with the constructors  and  destruc-
       tors of global C++ objects, particularly in the case where using atexit() or onexit(), for
       example).  As such, if you are writing a portable MPI program, you cannot  make	the  same
       assumptions that LAM/MPI does.

       In  general, it is safest to call MPI_Init (or MPI_Init_thread ) as soon as possible after
       main begins, and call MPI_Finalize immediately before the  program  is  supposed  to  end.
       Consult	the  documentation  for  each MPI implementation for their intialize and finalize

       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.
	      -  This error class is associated with an error code that indicates that an attempt
	      was made to call MPI_INIT a second time.	MPI_INIT may only be  called  once  in	a
	      - Other error; use MPI_Error_string to get more information about this error code.

       MPI_Init_thread, MPI_Finalize, lamboot, mpirun, lamhalt

       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_Init(3)
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