mpi_wtime(3openmpi) [osx man page]

MPI_Wtime(3OpenMPI)													       MPI_Wtime(3OpenMPI)

NAME

       MPI_Wtime - Returns an elapsed time on the calling processor.

SYNTAX

C Syntax
       #include <mpi.h>
       double MPI_Wtime()

Fortran Syntax
       INCLUDE 'mpif.h'
       DOUBLE PRECISION MPI_WTIME()

C++ Syntax
       #include <mpi.h>
       double Wtime()

RETURN VALUE

       Time in seconds since an arbitrary time in the past.

DESCRIPTION

       MPI_Wtime returns a floating-point number of seconds, representing elapsed wall-clock time since some time in the past.

       The  "time in the past" is guaranteed not to change during the life of the process. The user is responsible for converting large numbers of
       seconds to other units if they are preferred.

       This function is portable (it returns seconds, not "ticks"), it allows high resolution, and carries no unnecessary baggage. One	would  use
       it like this:

	   {
	      double starttime, endtime;
	      starttime = MPI_Wtime();
	       ....  stuff to be timed	...
	      endtime	= MPI_Wtime();
	      printf("That took %f seconds
",endtime-starttime);
	   }

       The times returned are local to the node that called them. There is no requirement that different nodes return the "same" time.

NOTES

       The  boolean variable MPI_WTIME_IS_GLOBAL, a predefined attribute key that indicates whether clocks are synchronized, does not have a valid
       value in Open MPI, as the clocks are not guaranteed to be synchronized.

       This is intended to be a high-resolution, elapsed (or wall) clock. See MPI_Wtick to determine the resolution of MPI_Wtime.

       This function does not return an error value. Consequently, the result of calling it before MPI_Init or after MPI_Finalize is undefined.

SEE ALSO

       MPI_Wtick

Open MPI 1.2							  September 2006					       MPI_Wtime(3OpenMPI)

MPI_Init(3OpenMPI)														MPI_Init(3OpenMPI)

NAME

       MPI_Init - Initializes the MPI execution environment

SYNTAX

C Syntax
       #include <mpi.h>
       int MPI_Init(int *argc, char ***argv)

Fortran Syntax
       INCLUDE 'mpif.h'
       MPI_INIT(IERROR)
	    INTEGER   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 any other MPI routine (apart from MPI_Initialized) is called. MPI can be initial-
       ized 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  nei-
       ther 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++ func-
       tions 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

Open MPI 1.2							  September 2006						MPI_Init(3OpenMPI)