/* 
 file: allgather.c
 compile: cc -64 allgather.c -lmpi
 run: mpirun -np 2 ./a.out

rank = 0 :  0  1  2  3 
  :  0  1  2  3  0  2  4  6  0  3  6  9  0  4  8 12 
rank = 1 :  0  2  4  6 
  :  0  1  2  3  0  2  4  6  0  3  6  9  0  4  8 12 
rank = 2 :  0  3  6  9 
  :  0  1  2  3  0  2  4  6  0  3  6  9  0  4  8 12 
rank = 3 :  0  4  8 12 
  :  0  1  2  3  0  2  4  6  0  3  6  9  0  4  8 12 
*/

#include "mpi.h" 
main( argc, argv ) 
int argc; 
char **argv; 
{ 

    int myrank; 
    int n;
    int i;

    int local_send[4];
    int local_recv[100];

    MPI_Init( &argc, &argv ); 
    MPI_Comm_rank( MPI_COMM_WORLD, &myrank ); 
    MPI_Comm_size( MPI_COMM_WORLD, &n ); 


    for(i=0; i<4; i++){
      local_send[i] = (myrank+1)*i;
    }
      
    MPI_Allgather(local_send,4, MPI_INT, local_recv, 4, 
         MPI_INT, MPI_COMM_WORLD);

    printf("rank = %d : ", myrank);
    for (i = 0; i< 4; i++) printf("%2d ", local_send[i]);
    printf("\n  : ");
    for (i = 0; i < 4*n; i++) 
    printf("%2d ", local_recv[i]);
    printf("\n");

    MPI_Finalize(); 
  }