/* 

sum1.c 

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

*/

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

#include <omp.h> 


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

  int NTHREADS = 10; 
  long n  =  atol(argv[1]); 
  double  sum;
  long  i; 
  double t1, t2; 
  
  //initialize sum 
  sum = 0; 

  t1 = omp_get_wtime(); 
  
  printf("Start. ");

  omp_set_num_threads(NTHREADS); 
#pragma omp parallel private(i) 
  {
    int nthreads = omp_get_num_threads(); 
    int thread_id = omp_get_thread_num(); 

    double mysum  = 0; //nitialize sum 

    //   printf("thread %d: \n", thread_id);
    for (i=thread_id; i<n; i += nthreads) {
      mysum  += atan(i); 
    }
  //mysum  is the local sum for thsi tread  
    
#pragma omp critical
    sum += mysum;
      
  }



  t2 = omp_get_wtime();   

  printf("sum=%.1f ", sum);
  printf("Done. time = %.1f\n",  t2-t1);
  
  return 0; 
}