/*  file: gather.c
    compile: cc -64 gather.c -lmpi
    run: mpirun -np 4 ./a.out
*/
#include "mpi.h" 
main( argc, argv ) 
int argc; 
char **argv; 
{ 
    int myrank; 

    int a[100];
    int i, j;
    int x[8];
    int n;

    MPI_Init( &argc, &argv ); 
    MPI_Comm_rank( MPI_COMM_WORLD, &myrank ); 
    MPI_Comm_size( MPI_COMM_WORLD, &n ); 
    /* 
       rank2 make: 2 3 4 5 6 7 8 9
       rank0 make: 0 1 2 3 4 5 6 7
       rank1 make: 1 2 3 4 5 6 7 8
       rank3 make: 3 4 5 6 7 8 9 10
    */
    printf("rank%d make:", myrank);
    for (i=0; i<8; i++){
      x[i]=myrank+i;
      printf(" %d", x[i]);
    }
    printf("\n");
    MPI_Gather(x, 8, MPI_INT, a, 8, MPI_INT, 0, MPI_COMM_WORLD);
    /*
       rank0 gather:
       0  1  2  3  4  5  6  7 
       1  2  3  4  5  6  7  8 
       2  3  4  5  6  7  8  9 
       3  4  5  6  7  8  9 10 
       */
    if (myrank == 0){
      printf("rank0 gather:\n");
      for (i=0; i<n; i++){
	for (j=0; j<8; j++) printf("%2d ", a[8*i+j]);
	printf("\n");
      }
      printf("\n");
    }
      
    MPI_Finalize(); 
  }