/* ///////////////////////////////////////////////////////////////////// */
/*! 
  \file  
  \brief Subarray example.

  Proc #0 creates a large array Abig with NROWS rows and NCOLS columns.
  Proc #1 receives a subarray with nrows_sub rows and ncols_sub
  columns starting at starts[].
  
  \author A. Mignone (mignone@to.infn.it)
  \date   March 14, 2020
*/
/* ///////////////////////////////////////////////////////////////////// */
#include <stdio.h>
#include <stdlib.h>
#include <mpi.h>
#include "tools.c"

#define NROWS   5
#define NCOLS   6

int main(int argc, char **argv)
{
  int i,j;
  int rank, size;
  int nrows_sub = 3;
  int ncols_sub = 2;
  int starts[2]    = {1,3};
  int subsizes[2]  = {nrows_sub,ncols_sub};
  int bigsizes[2]  = {NROWS, NCOLS};
  int **Abig;
  int **Asub;
  MPI_Datatype MPI_Subarr;

/* --------------------------------------------------------
   0. Initialize the MPI execution environment,
      create subarray type
   -------------------------------------------------------- */

  MPI_Init(&argc, &argv);
  MPI_Comm_rank(MPI_COMM_WORLD, &rank);
  MPI_Comm_size(MPI_COMM_WORLD, &size);

  MPI_Type_create_subarray(2, bigsizes, subsizes, starts,
                           MPI_ORDER_C, MPI_INT, &MPI_Subarr);
  MPI_Type_commit(&MPI_Subarr);

  if (size < 2) {
    if (rank == 0){
      fprintf(stderr,"! Need at least 2  processors.\n");
    }
    MPI_Finalize();
    return 1;
  }

/* --------------------------------------------------------
   1. Proc #0 creates the big array,
      Proc #1 receives the subarray.
   -------------------------------------------------------- */

  if (rank == 0) {
    Abig = Allocate_2DintArray(NROWS, NCOLS);

  /* -- 1a. Fill array -- */

    for (i = 0; i < NROWS; i++){
    for (j = 0; j < NCOLS; j++){
      Abig[i][j] = j + i*NCOLS;
    }}

  /* -- 1b. Show array -- */

    Show_2DintArray(Abig, NROWS, NCOLS, "Big array (proc #0):");

    MPI_Send(&(Abig[0][0]), 1, MPI_Subarr, 1, 123, MPI_COMM_WORLD);

    free(Abig[0]);
    free(Abig);

  } else if (rank == 1) {

    Asub = Allocate_2DintArray(nrows_sub, ncols_sub);

    MPI_Recv(&(Asub[0][0]), nrows_sub*ncols_sub, MPI_INT, 0,
             123, MPI_COMM_WORLD, MPI_STATUS_IGNORE);

    Show_2DintArray(Asub, nrows_sub, ncols_sub, "Received subarray (proc #1):");

    free(Asub[0]);
    free(Asub);
  }

  MPI_Type_free(&MPI_Subarr);
  MPI_Finalize();
  return 0;
}