#include "mpi.h"
#include <stdio.h>
#include <math.h>

int main(int argc,char *argv[])
{
    int done = 0, n, myid, numprocs, i;
    double PI25DT = 3.141592653589793238462643;
    double mypi, pi, h, sum, x, mflops;
    double startwtime = 0.0, endwtime;
    int  namelen;
    char processor_name[MPI_MAX_PROCESSOR_NAME];

    /* set up MPI and get number of processes, the current id,
       and the processor (node) name */

    MPI_Init(&argc,&argv);
    MPI_Comm_size(MPI_COMM_WORLD,&numprocs);
    MPI_Comm_rank(MPI_COMM_WORLD,&myid);
    MPI_Get_processor_name(processor_name,&namelen);

    /* if we don't get the right number of arguments, print help
       string (if we're the master node) and exit (all nodes) */

    if (argc != 2) {
	if (myid == 0) {
	        printf("Usage: mpirun -np <numproc> %s <loopcount>\n");
	}
        MPI_Finalize();
        exit(0);
    }

    /* print out MPI info for each node */

    printf("Process %d of %d on %s\n", myid, numprocs, processor_name);

    /* get loop counter from argument list */

    n = atoi(argv[1]);

    /* if we're the master, get the start time */
    if (myid == 0) {
	    startwtime = MPI_Wtime();
    }

    MPI_Bcast(&n, 1, MPI_INT, 0, MPI_COMM_WORLD);
    h   = 1.0 / (double) n;
    sum = 0.0;

    /* step through the loop, from myid to n, stepping numprocs */
    /* A slightly better approach starts from large i and works back */
    for (i = myid + 1; i <= n; i += numprocs) {
        x = h * ((double)i - 0.5);
        sum += ( 4.0 / ( 1.0 + x * x ));
    }
    mypi = h * sum;

    /* we're done, gather the results from all the nodes and sum them up */
    MPI_Reduce(&mypi, &pi, 1, MPI_DOUBLE, MPI_SUM, 0, MPI_COMM_WORLD);

    /* if we're the master, print out the results */
    if (myid == 0) {
        printf("pi is approximately %.16f, Error is %.16f\n", pi, fabs(pi - PI25DT));
        endwtime = MPI_Wtime();
        printf("wall clock time = %f\n", endwtime-startwtime);	       
        mflops = ((6.0 * (double)n) / (endwtime - startwtime)) / 1000000.0;
        printf("Estimated MFLOPs = %f\n", mflops);
        fflush( stdout );
    }
    /* shut down MPI *?
    MPI_Finalize();

    /* exit the program */
    return 0;

} /* end main */