/* 

sum6.c 

compute sum = atan(1) + atan(2) + ... + atan(n)
 */

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

#include <omp.h> 

#define NUM_THREADS 4

int main(int argc, char** argv) {

  long n  = 100000000; 
  double  sum; 
  long  i; 
  double t1, t2; 

  t1 = omp_get_wtime(); 

  //initialize sum 
  sum = 0; 

omp_set_num_threads(NUM_THREADS); 
#pragma omp parallel  private (i)
  { 
    double local_sum = 0; 

    int thread_id = omp_get_thread_num(); 
    printf("Start(%d)\n", thread_id); 
    
#pragma omp for 
    for (i=0; i<n; i++) {
       local_sum   +=  atan(i); 
    }//for 

 #pragma omp critical 
    sum += local_sum;
      
    printf("Done(%d)\n", thread_id); 
  } //end parallel  
				      
  t2 = omp_get_wtime();   
 
  printf("sum=%.1f ", sum);
  printf("Done. time = %.1f\n",  t2-t1);
  
  return 0; 
}