/* L-5 MCS 572 Friday 20 January 2012 : illustration of send/receive
 * This program illustrates the MPI_Send and MPI_Recv to
 * compute the square of the first p even numbers, using p processors. */

#include <stdio.h>
#include <stdlib.h>
#include <mpi.h>

#define v 1 /* verbose flag, output if 1,
                          no output if 0 */

#define tag 100 /* tag for sending a number */

int main ( int argc, char *argv[] )
{
   int p,myid,i,f,*x;
   MPI_Status status;

   MPI_Init(&argc,&argv);
   MPI_Comm_size(MPI_COMM_WORLD,&p);
   MPI_Comm_rank(MPI_COMM_WORLD,&myid);

   if(myid == 0) /* the manager allocates
                    and initializes x */
   {
      x = (int*)calloc(p,sizeof(int));
      x[0] = 2;
      for (i=1; i<p; i++) x[i] = 2*x[i-1];
      if(v>0)
      {
         printf("The data to square : ");
         for (i=0; i<p; i++)
            printf(" %d",x[i]); printf("\n");
      }
   }

   if(myid == 0) /* the manager copies x[0] to f */
   {             /* and sends the i-th element to 
                    the i-th processor */
      f = x[0]; 
      for(i=1; i<p; i++)
         MPI_Send(&x[i],1,MPI_INT,i,tag,MPI_COMM_WORLD);
   }
   else  /* every worker receives its f from the manager */
   {
      MPI_Recv(&f,1,MPI_INT,0,tag,MPI_COMM_WORLD,&status);
      if(v>0) printf("Node %d will square %d\n",myid,f);
   }
   f *= f;       /* every node does the squaring */

   if(myid == 0) /* the manager receives f in x[i]
                    from processor i */
      for(i=1; i<p; i++)
         MPI_Recv(&x[i],1,MPI_INT,i,tag,MPI_COMM_WORLD,
                  &status);
   else     /* every worker sends f to the manager */
      MPI_Send(&f,1,MPI_INT,0,tag,MPI_COMM_WORLD);
 
   if(myid == 0) /* the manager prints the final results */
   {
      x[0] = f;
      printf("The squared numbers : ");
      for(i=0; i<p; i++) printf(" %d",x[i]);
      printf("\n");
   }

   MPI_Finalize();
   return 0;
}