# include <stdlib.h>
# include <stdio.h>
# include <math.h>
# include <time.h>
/*
  CHANGE 1) Include the OMP.H file here;
# include <omp.h>
*/

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

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

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

    MAIN is the main program for QUAD.

  Discussion:

    QUAD is a C program to estimate the integral of
      f = 50.0 / ( pi * ( 2500.0 * x[i] * x[i] + 1.0 ) )
    between 0 and 10.

    If you modify the program in 4 places, it should run correctly
    under OpenMP.

    If you can do that, then compare the execution time when you
    use 1, 2, 4 or 8 threads.
 
  Licensing:

    This code is distributed under the GNU LGPL license. 

  Modified:

    03 September 2013

  Author:

    John Burkardt
*/
{
  double a = 0.0;
  double b = 10.0;
  double error;
  double exact = 0.49936338107645674464;
  int i;
  int n = 1000000;
  double pi = 3.141592653589793;
  double total;
  double wtime = 0.0;
  double *x;

  printf ( "\n" );
  printf ( "QUAD:\n" );
  printf ( "  C version\n" );
  printf ( "\n" );
  printf ( "  Estimate the integral of f(x) from A to B.\n" );
  printf ( "  f(x) = 50 / ( pi * ( 2500 * x * x + 1 ) ).\n" );
  printf ( "  A = %f\n", a );
  printf ( "  B = %f\n", b );
  printf ( "  Exact integral from 0 to 10 is 0.49936338107645674464...\n" );
/*
  Load the array X with evenly spaced values between A and B.
*/
  x = ( double * ) malloc ( n * sizeof ( double ) );

  for ( i = 0; i < n; i++ )
  {
    x[i] =  ( ( double ) ( n - i - 1 ) * a   
            + ( double ) (     i     ) * b ) 
            / ( double ) ( n     - 1 );
  }
/*
  Evaluate F at each node, sum and average.
*/
/*
  CHANGE 2) Use the OpenMP timer here to initialize WTIME.
*/

/* wtime = ??? */

  total = 0.0;
/*
  CHANGE 3) Fill in these two OpenMP directives here.
*/

# pragma omp parallel private ( ? ) shared ( ? )
# pragma omp for ???

  for ( i = 0; i < n; i++ )
  {
    total = total + 50.0 / ( pi * ( 2500.0 * x[i] * x[i] + 1.0 ) );
  }
  total = ( b - a ) * total / ( double ) n;
/*
  CHANGE 4) Call the OpenMP timer here to update WTIME.
*/

/*  wtime = ??? */


/*
  Print quadrature estimate, error, time
*/
  error = fabs ( total - exact );

  printf ( "\n" );
  printf ( "  Estimate = %f\n", total );
  printf ( "  Error    = %e\n", error );
  printf ( "  Wallclock time   = %f\n", wtime );

  free ( x );

  return 0;
}