/* =====================================================
   MPI example: find max and min in array
   ===================================================== */


#include <iostream.h>
#include <stdlib.h>
#include <sys/time.h>
#include <mpi.h>

struct timeval start_time, stop_time;
int elapsed;


#define MAX  100000000

int    num_procs;
double x[MAX];

int main(int argc, char *argv[])
{
   char *s;
   int i, n;
   int start, stop;
   int myid;
   double my_min, others_min[10];
   double my_max, others_max[10];

   MPI_Request rq_min[10];
   MPI_Request rq_max[10];

   MPI_Init(&argc,&argv);                      // Initialize

   MPI_Comm_size(MPI_COMM_WORLD, &num_procs);  // Get # processors
   MPI_Comm_rank(MPI_COMM_WORLD, &myid);       // Get my rank (id)


   /* -------------------------
      Generate random number
      ------------------------- */
   for (i = 0; i < MAX; i++)
      x[i] = random()/(double)1147483648;


   if ( myid == 0 )
      cout << "Using " << num_procs << " processes..." << endl << endl;

   gettimeofday(&start_time, NULL);

   /* ******************************************************************* */
   /* --------------------------------------
      Find the min. among my numbers

      The min is stored in min[s]
      -------------------------------------- */

   n = MAX/num_procs;


   start = myid * n;

   if ( myid != (num_procs-1) )
   {
      stop = start + n;
   }
   else
   {
      stop = MAX;
   }

   my_min = x[start];

   for (i = start+1; i < stop; i = i + n )
   {
      if ( x[i] < my_min )
            my_min = x[i];
   }

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


   if ( myid == 0 )
   {
      cout << "Done... Now collecting output from others" << endl;

      /* ----------------------------------------------
         Start getting the min from others.....
         ---------------------------------------------- */
      for (i = 1; i < num_procs; i++)
      {
         MPI_Irecv(&others_min[i], 1, MPI_DOUBLE,i,0, MPI_COMM_WORLD, 
		&rq_min[i]);
      }
   }
   else
   {
      MPI_Isend(&my_min, 1, MPI_DOUBLE, 0, 0, MPI_COMM_WORLD, &rq_min[0]); 
   }


   /* -----------------------------------------------
      -----------------------------------------------
      Now find the max
      -----------------------------------------------
      ----------------------------------------------- */

   my_max = x[start];

   for (i = start+1; i < stop; i = i + n )
   {
      if ( x[i] > my_max )
            my_max = x[i];
   }

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


   if ( myid == 0 )
   {
      /* -------------------------------------
         Get the max from others and compare
         ------------------------------------- */
      for (i = 1; i < num_procs; i++)
      {

         MPI_Irecv(&others_max[i], 1, MPI_DOUBLE,i,0, MPI_COMM_WORLD, 
		&rq_max[i]);
      }

   }
   else
   {
      MPI_Send(&my_max, 1, MPI_DOUBLE, 0, 0, MPI_COMM_WORLD); 
   }

   if ( myid == 0 )
   {
      cout << "Done... Now collecting output from others" << endl;

      for ( i = 1; i < num_procs; i++)
      {
	 MPI_Wait( &rq_min[i], NULL );

         cout << "Min received from proc " << i << " = "<<others_min[i] << endl;

         if ( others_min[i] < my_min )
            my_min = others_min[i];
      }

      for ( i = 1; i < num_procs; i++)
      {
	 MPI_Wait( &rq_max[i], NULL );

         cout << "Max received from proc " << i << " = "<<others_max[i] << endl;

         if ( others_max[i] > my_max )
            my_max = others_max[i];
      }

      gettimeofday(&stop_time, NULL);

      elapsed = (stop_time.tv_sec*1000000 + stop_time.tv_usec) -
                (start_time.tv_sec*1000000 + start_time.tv_usec);

      cout << "min = " << my_min << endl << endl;
      cout << "max = " << my_max << endl << endl;
      cout << "Elapsed time = " << elapsed << " microseconds" << endl;
   }
   else
   {
      MPI_Wait( &rq_min[0], NULL );
      MPI_Wait( &rq_max[0], NULL );
   }
   MPI_Finalize();
}