/*
 file: gatherv.c
 compile: cc gatherv.c -lmpi
 run: mpirun -np 4 ./a.out
*/

#include "mpi.h" 
main( argc, argv ) 
int argc; 
char **argv; 
{ 
    int myrank; 
    int gsize,sendarray[10]; 
    int root, *rbuf, stride; 
    int *displs,i,*rcounts; 

    stride = 12;
    root = 0;

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

    /*
       send data of rank0 0 1 2 3 4 5 6 7 8 9
       send data of rank1 1 2 3 4 5 6 7 8 9 10
       send data of rank2 2 3 4 5 6 7 8 9 10 11
       send data of rank3 3 4 5 6 7 8 9 10 11 12
       */
    
    printf("send data of rank%d", myrank);
    for(i=0; i<10; i++){
      sendarray[i] = myrank+i;
      printf(" %d", sendarray[i]);
    }
    printf("\n");

    if(myrank == root){
      rbuf = (int *)malloc(gsize*stride*sizeof(int)); 
      displs = (int *)malloc(gsize*sizeof(int)); 
      rcounts = (int *)malloc(gsize*sizeof(int)); 
      for (i=0; i<gsize; ++i) { 
        displs[i] = i*stride; 
        rcounts[i] = 10; 
      } 
    }
    MPI_Gatherv( sendarray, 10, MPI_INT, rbuf, rcounts, displs,  MPI_INT, 
                   root, MPI_COMM_WORLD);

    /*
       rank0 receive:
       0 1 2 3 4 5 6 7 8 9 2 0 1 
       2 3 4 5 6 7 8 9 10 11 4 2 
       3 4 5 6 7 8 9 10 11 0 0 3 
       4 5 6 7 8 9 10 11 12 11 4 
      */
    if(myrank == root){
        printf("rank0 receive:\n");
      	for(i=0; i<gsize*stride; i++){
      	    printf("%d ", rbuf[i]);
	    if (i != 0 && i%stride == 0) printf("\n");
    	}
    	printf("\n");
	}
    MPI_Finalize(); 
  }