# include <stdlib.h>
# include <stdio.h>
# include <omp.h>
# include <time.h>

int main ( int argc, char *argv[] );

/******************************************************************************/

int main ( int argc, char *argv[] )

/******************************************************************************/
/*
  Purpose:

    HELLO has each thread print out its ID.

  Discussion:

    HELLO is a "Hello, World" program for OpenMP.

    But we demonstrate a few simple features of OpenMP, including:

    How you get the "include" file.
    How you measure wall clock time.
    How you find out how many processors are available.
    How you find out which thread you are in a parallel section.
    How you find out how many threads are available in a parallel section.
    How you set the number of threads.

  Licensing:

    This code is distributed under the GNU LGPL license. 

  Modified:

    20 November 2007

  Author:

    John Burkardt
*/
{
  int id;
  int proc_num;
  int thread_num;
  double wtime;
  double wtime1;
  double wtime2;

  printf ( "\n" );
  printf ( "HELLO\n" );
  printf ( "  C/OpenMP version\n" );

  wtime1 = omp_get_wtime ( );
/*
  How many processors are available?
*/
  proc_num = omp_get_num_procs ( );

  printf ( "\n" );
  printf ( "  The number of processors available:\n" );
  printf ( "  OMP_GET_NUM_PROCS () = %d\n", proc_num );
/*
  How many threads are available by default or environment setting?
*/
#pragma omp parallel private ( id )
  {
    id = omp_get_thread_num ( );
    thread_num = omp_get_num_threads ( );

    if ( id == 0 )
    {
      printf ( "\n" );
      printf ( "  Calling OMP_GET_NUM_THREADS inside a\n" );
      printf ( "  parallel region, we get the number of\n" );
      printf ( "  threads is %d\n", thread_num );
    }
    printf ("  This is process %d out of %d\n", id, thread_num );
  }
/*
  Request double the number of threads.
*/
  thread_num = 2 * thread_num;

  printf ( "\n" );
  printf ( "  We request %d threads.\n", thread_num );

  omp_set_num_threads ( thread_num );
/*
  Now how many threads do we see?
*/
#pragma omp parallel private ( id )
  {
    id = omp_get_thread_num ( );
    thread_num = omp_get_num_threads ( );

    if ( id == 0 )
    {
      printf ( "\n" );
      printf ( "  Calling OMP_GET_NUM_THREADS inside a\n" );
      printf ( "  parallel region, we get the number of\n" );
      printf ( "  threads is %d\n", thread_num );
    }
    printf ("  This is process %d out of %d\n", id, thread_num );
  }
/*
  Finish up by measuring the elapsed time.
*/
  wtime2 = omp_get_wtime ( );
  wtime = wtime2 - wtime1;

  printf ( "\n" );
  printf ( "HELLO\n" );
  printf ( "  Normal end of execution.\n" );

  printf ( "\n" );
  printf ( "  Elapsed wall clock time = %f\n", wtime );

  return 0;
}