#include <stdio.h>
#include <stdlib.h>
#include <iostream>
#include <mpi.h>
#include <math.h>
using namespace std;

int main(int argc, char *argv[]) {
    int tid, nthreads;
    char *cpu_name;
    double time_initial, time_current, time;


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

    int n=10000, i;
    double PI25DT = 3.141592653589793238462643;
    double mypi, pi, h, sum, x;


    MPI_Init(&argc, &argv);
    time_initial = MPI_Wtime();
    MPI_Comm_rank(MPI_COMM_WORLD, &tid);
    MPI_Comm_size(MPI_COMM_WORLD, &nthreads);
    cpu_name = (char *) calloc(80, sizeof(char));
    gethostname(cpu_name, 80);

   while (1) {
    if (tid == 0) {
        cout << "Enter the number of intervals: (0 quits)"
         << endl;
        cin >> n;

    }
    MPI::COMM_WORLD.Bcast(&n, 1, MPI::INT, 0);
    if (n==0)
        break;
    else {
        h = 1.0 / (double) n;
        sum = 0.0;
        for ( i = tid + 1; i <= n; i++ ) {
            x = h * ((double)i - 0.5);
            sum += (4.0 / (1.0 + x*x));
        }
        mypi = h * sum;

        MPI::COMM_WORLD.Reduce(&mypi, &pi, 1, MPI::DOUBLE,
               MPI::SUM, 0);
        time_current = MPI_Wtime();
        time = time_current - time_initial;
        printf("tid %i wait time=%.3f on machine=%s [NCPU=%i]\n",
                    tid , time, cpu_name, nthreads);
        if (tid == 0){
            printf("pi calculated: %.25f \nand real pi is %.25f \n", pi, PI25DT);
            cout<< "Error is "<<fabs(pi - PI25DT) <<endl;
        }
    }
    }

/////////////////////////////////////////////////////////////////////////////
/*int loop_min, loop_max , i , n=2;
double inf = 100000000, sum =0, p_sum=0;

for(tid=0; tid < nthreads ; tid++)
{
    loop_min    = 1 +  (int)((tid + 0)  *  (inf-1)/nthreads);
    loop_max    =      (int)((tid + 1)  *  (inf-1)/nthreads);

    for(i=loop_max-1;i>=loop_min;i--)
    {
        p_sum += 1.0/pow(i,(double)n);
    }

}
MPI_Reduce(&p_sum,&sum,1,MPI_DOUBLE,MPI_SUM,0,MPI_COMM_WORLD);
*/
///////////////////////////////////////////////////////////////
/////////////////////////////////////////////////////////////

//    printf("zeta(2):%f\n",sum);
    MPI_Finalize();
//    printf("final zeta(2):%f\n",sum);
    return (0);
}