#include <stdio.h>
#include <stdarg.h>
#include <time.h>
/* get definition of MPI constants */
#include "mpi.h"
#define NINT 1000000000

void adder(int *, int *, double *, double *);

int main (int argc, char *argv[])
/* This program calculates the variance of the first 10^9 integers     */
/* using MPI with multiple Macintoshes.                                 */
{
int n, start;
clock_t start_program, end_program;
double sum1, sum2, mean, mesq;
int ierror, nproc, idproc, root=0;
double partial[2], result[2];

/* initialize the MPI environment */
ierror = MPI_Init(&argc, &argv);
ierror = MPI_Comm_size(MPI_COMM_WORLD,&nproc);
ierror = MPI_Comm_rank(MPI_COMM_WORLD,&idproc);

start_program = clock ();

/* set arguments for each node, last node might have more work */
n = NINT / nproc;
start = n * idproc;
n += start;
if (idproc == (nproc-1))
   n = NINT;

adder (&n, &start, &sum1, &sum2);

/* add up all the partial sums from each node */
partial[0] = sum1;
partial[1] = sum2;
ierror = MPI_Reduce(partial,result,2,MPI_DOUBLE,MPI_SUM,root,
                    MPI_COMM_WORLD);

/* terminate MPI environment */
ierror = MPI_Barrier(MPI_COMM_WORLD);
ierror = MPI_Finalize();

/* node 0 has the results */
if (idproc == root) {
   n = NINT;
   mean = result[0] / n;
   mesq = result[1] / n;
   printf("%15d %20.3f %20.3f\n", n, mean, mesq - (mean * mean));
}

end_program = clock ();

printf("\ntime in sec: %7.2f\n", (end_program-start_program)/60.);
if (idproc == root) {
   printf("hit carriage return to continue\n");
   getchar();
}
return 0;
}



void
adder (int *n, int *start, double *s1, double *s2)
{
int i;
double ls1 = 0.0, ls2 = 0.0;
for (i=(*start);i<(*n);i++)
   {
      ls1+=(double) i;
      ls2+=(double) i*i;
   }
*s1 = ls1;
*s2 = ls2;
}