MPI_Wtime(3)                       Open MPI                       MPI_Wtime(3)



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 MPI::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\n",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 function is intended to be a high-resolution, elapsed (or wall)
       clock. See MPI_Wtick to determine the resolution of MPI_Wtime.

       On POSIX platforms, this function may utilize a timer that is cheaper
       to invoke than the gettimeofday() system call, but will fall back to
       gettimeofday() if a cheap high-resolution timer is not available.  The
       ompi_info command can be consulted to see if Open MPI supports a native
       high-resolution timer on your platform; see the value for "MPI_WTIME
       support" (or "options:mpi-wtime" when viewing the parsable output).  If
       this value is "native", a method that is likely to be cheaper than
       gettimeofday() will be used to obtain the time when MPI_Wtime is
       invoked.

       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




1.4.1                            Jan 14, 2010                     MPI_Wtime(3)
