/* L-16 MCS 572 Wednesday 15 February 2006 : pipelining to sum numbers.
 * This program illustrates the pipelining to sum p*(p+1) numbers. */

#include <stdio.h>
#include "mpi.h"
#define tag 100  /* tag for sending a number */
#define v 1 /* verbose flag, output if 1, no output if 0 */

void pipeline_sum ( int i, int p );
/* performs a pipeline sum of p*(p+1) numbers */

int main ( int argc, char *argv[] )
{
   int i,p;

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

   pipeline_sum(i,p);

   MPI_Finalize();

   return 0;
}

void pipeline_sum ( int i, int p )
{
   int n[p][p-i+1];
   int j,k;
   MPI_Status status;

   if(i==0)  /* manager generates numbers */
   {
      for(j=0; j<p; j++) for(k=0; k<p+1; k++) n[j][k] = (p+1)*j+k+1;
      if(v>0)
      {
         printf("The data to sum : ");
         for(j=0; j<p; j++) for(k=0; k<p+1; k++) printf(" %d",n[j][k]);
	 printf("\n");
      }
   }

   for(j=0; j<p; j++)
      if(i==0)  /* manager starts pipeline of j-th sequence */
      {
         n[j][1] += n[j][0];
         printf("Manager starts pipeline for sequence %d...\n",j);
         MPI_Send(&n[j][1],p,MPI_INT,1,tag,MPI_COMM_WORLD);
         MPI_Recv(&n[j][0],1,MPI_INT,p-1,tag,MPI_COMM_WORLD,&status);
         printf("Manager received sum %d.\n",n[j][0]);
      }
      else      /* worker i receives p-i+1 numbers */
      {
         MPI_Recv(&n[j][0],p-i+1,MPI_INT,i-1,tag,MPI_COMM_WORLD,&status);
         printf("Processor %d receives sequence %d : ",i,j);
         for(k=0; k<p-i+1; k++) printf(" %d", n[j][k]); printf("\n");
         n[j][1] += n[j][0]; 
         if(i < p-1)
            MPI_Send(&n[j][1],p-i,MPI_INT,i+1,tag,MPI_COMM_WORLD);
         else
            MPI_Send(&n[j][1],1,MPI_INT,0,tag,MPI_COMM_WORLD);
      }

   if(i==0)  /* manager computes the total sum */
   {
      for(j=1; j<p; j++) n[0][0] += n[j][0];
      printf("The total sum : %d\n",n[0][0]);
   }
}