# include <stdio.h>
# include <stdlib.h>
# include <math.h>

double f ( int m, double x[] );

int main ( int argc, char* argv[] )
{
  double error;
  double f1;
  double f2;
  int i;
  int j;
  int m = 2;
  int n = 1000000;
  unsigned int seed = 123456789;
  double stdev;
  double sterr;
  double value;
  double x[2];

  seed = time ( 0 );
  srand ( seed );

  f1 = 0.0;
  f2 = 0.0;

  for ( i = 0; i < n; i++)
  {
    for ( j = 0; j < m; j++ )
    {
      x[j] = ( double ) rand ( ) / ( double ) RAND_MAX;
    }
    value  = f ( m, x );
    f1 = f1 + value;
    f2 = f2 + value * value;
  }

  f1 = f1 / ( double ) n;
  f2 = f2 / ( double ) ( n - 1 );
  stdev = sqrt ( f2 - f1 * f1 );
  sterr = stdev / sqrt ( ( double ) n );
  error = fabs ( f1 - 1.0 );

  printf ( "\n" );
  printf ( "      N          F           stdev   sterr      err\n" );
  printf ( "\n" );
  printf ( "%7d  %.15g  %6.4f  %6.4f  %8g\n", n, f1, stdev, sterr, error );

  return 0;
}
double f ( int m, double x[] )
{
  int i;
  double value;

  value = 1.0;
  for ( i = 0; i < m; i++ )
  {
//  value = value + x[i] * x[i];  
    value = value * fabs ( 4.0 * x[i] - 2.0 );
  }
//value = sqrt ( value );

  return value;
}