/* Program pi_scale.c */

#include "mpi.h"
#include <stdio.h>
#include <math.h>
static inline int max(int a, int b) {
  return a > b ? a : b;
}
int main( int argc, char *argv[] )
{
  int n, myid, numprocs, i, j, nt;
    double PI25DT = 3.141592653589793238462643;
    double mypi, pi, h, sum, x;
    double t_start, t_endpar, t_endcom, t_endser;
    double res, speedup, s_Amdahl;
    MPI_Init(&argc,&argv);
    MPI_Comm_size(MPI_COMM_WORLD,&numprocs);
    MPI_Comm_rank(MPI_COMM_WORLD,&myid);
    double t_all[numprocs];
    double t_par[numprocs];
    double t_com[numprocs];
    double t_ser[numprocs];
    while (1) {
        if (myid == 0) {
            printf("Enter the number of intervals: (0 quits) ");
            scanf("%d",&n);
        }
        MPI_Bcast(&n, 1, MPI_INT, 0, MPI_COMM_WORLD);
        if (n == 0)
            break;
        else {
            h   = 1.0 / (double) n;
            for (j = -3; j < numprocs; j++) {
                /* negative j's are serial warm-ups */
                nt = max(0,j) + 1;
                t_start = MPI_Wtime();
                sum = 0.0;
                if (myid < nt) {
                    for (i = myid + 1; i <= n; i += nt) {
                        x = h * ((double)i - 0.5);
                        sum += (4.0 / (1.0 + x*x));
                    }
                }
                mypi = h * sum;
                t_endpar = MPI_Wtime();
                MPI_Reduce(&mypi, &pi, 1, MPI_DOUBLE, MPI_SUM, 0,
                           MPI_COMM_WORLD);
                t_endcom = MPI_Wtime();
                if (myid == 0) {
                    printf("%3d tasks: ", nt);
                    printf("pi is approximately %.16f, ", pi);
                    printf("Error is %.16f\n", fabs(pi - PI25DT));
                    t_endser = MPI_Wtime();
                    t_all[nt-1] = t_endser - t_start;
                    t_par[nt-1] = t_endpar - t_start;
                    t_com[nt-1] = t_endcom - t_endpar;
                    t_ser[nt-1] = t_endser - t_endcom;
                }
            }
        }
        if (myid == 0) {
            res = MPI_Wtick();
            printf("Clock resolution is %.10f\n", res);
            printf(" nt     t_all        t_par        t_com");
            printf("        t_ser       speedup    s_Amdahl\n");
            for (j = 0; j < numprocs; j++) {
                speedup = t_all[0]/t_all[j];
                s_Amdahl = t_all[0]/(t_ser[0] + t_com[0] +
                                     t_par[0]/(double)(j+1));
                printf("%3d %12.9f %12.9f %12.9f %12.9f", j+1,
                        t_all[j], t_par[j], t_com[j], t_ser[j]);
                printf("%11.4f %11.4f\n", speedup, s_Amdahl);
            }
        }
    }
    MPI_Finalize();
    return 0;
}