! http://www.llnl.gov/computing/tutorials/openMP/exercise.html

!******************************************************************************
! FILE: omp_hello.f
! DESCRIPTION:
!   OpenMP Example - Hello World - Fortran Version
!   In this simple example, the master thread forks a parallel region.
!   All threads in the team obtain their unique thread number and print it.
!   The master thread only prints the total number of threads.  Two OpenMP
!   library routines are used to obtain the number of threads and each
!   thread's number.
! AUTHOR: Blaise Barney  5/99
! LAST REVISED: 
!******************************************************************************

      PROGRAM HELLO

      INTEGER NTHREADS, TID, OMP_GET_NUM_THREADS, &
              OMP_GET_THREAD_NUM

!     Fork a team of threads giving them their own copies of variables
!$OMP PARALLEL PRIVATE(NTHREADS, TID)


!     Obtain thread number
      TID = OMP_GET_THREAD_NUM()
      PRINT *, 'Hello World from thread = ', TID

!     Only master thread does this
      IF (TID .EQ. 0) THEN
        NTHREADS = OMP_GET_NUM_THREADS()
        PRINT *, 'Number of threads = ', NTHREADS
      END IF

!     All threads join master thread and disband
!$OMP END PARALLEL

      END

!*****************
!
! f90 omp_hello.f90     <-- Compiling this OpenMP file

! ./a.out        <-- Running this OpenMP executable

!  Hello World from thread =  0
!  Hello World from thread =  1
!  Number of threads =  4
!  Hello World from thread =  2
!  Hello World from thread =  3

! OMP_NUM_THREADS=8    <-- Changing the number of threads

! ./a.out             <-- Running the executable again

!  Hello World from thread =  0
!  Hello World from thread =  1
!  Number of threads =  8
!  Hello World from thread =  2
!  Hello World from thread =  3
!  Hello World from thread =  4
!  Hello World from thread =  5
!  Hello World from thread =  6
!  Hello World from thread =  7