/*
 * Open Systems Laboratory
 * http://www.lam-mpi.org/tutorials/
 * Indiana University
 *
 * MPI Tutorial
 * Lab - Datatypes
 *
 * Mail questions regarding tutorial material to lam at lam dash mpi dot org
 */

/* 
 * Create a datatype called submatrix that consists of elements in
 * alternate rows and alternate columns of the given original matrix.
 *
 * Use MPI_SENDRECV to send the submatrix to itself and print the
 * results. To test this program you can run the program on just
 * one processor.
 *
 * For example, if the given matrix is:
 *
 * 1  2  3   4  5  6
 * 7  8  9  10 11 12
 * 13 14 15 16 17 18
 * 19 20 21 22 23 23
 * 24 25 26 27 28 29
 *
 * The submatrix created should look like:
 *
 * 1   3  5
 * 13 15 17
 * 24 26 28
 *
 */

#include <stdio.h>
#include <mpi.h>

 
int 
main(int argc, char *argv[])
{
  int myrank, size;
  int i, j, mym = 10, myn = 10;
  int a[10][10], b[5][5], c[5][5];
  MPI_Datatype subrow, submatrix;
  MPI_Aint sizeofint;
  
  MPI_Init (&argc, &argv);
  MPI_Comm_rank (MPI_COMM_WORLD, &myrank);
  MPI_Comm_size (MPI_COMM_WORLD, &size);
  
  /* Initialize the local array */

  for (i = 0; i < mym; ++i)
    for (j = 0; j < myn; ++j)
      a[i][j] = i * myn + j + 1;
  
  /* Print the local matrix */

  if (myrank == 0) {
    for (i = 0; i < mym; ++i) {
      for (j = 0; j < myn; ++j)
	printf("%d ", a[i][j]);
      printf("\n");
    }
  }
  
  /* Create a submatrix datatype */

  MPI_Type_extent(MPI_INT, &sizeofint);
  
  /* Create datatype for the sub-row */

  MPI_Type_vector(5, 1, 2, MPI_INT, &subrow);

  /* Commit the datatype created */

  MPI_Type_commit(&subrow);
  
  /* Create datatype for the sub-matrix */

  MPI_Type_hvector(5, 1, 20*sizeofint, subrow, &submatrix);
  
  /* Commit the datatype created */

  MPI_Type_commit(&submatrix);
  
  /* Send it to self and print it */

  MPI_Sendrecv(a, 1, submatrix, myrank, 0, c, 5 * 5, MPI_INT, myrank, 0,
		 MPI_COMM_WORLD, MPI_STATUS_IGNORE);
  
  /* Print the submatrix */

  if (myrank == 0) {
    for (i = 0; i < 5; ++i) {
      for (j = 0; j < 5; ++j)
	printf("%d ", c[i][j]);
      printf("\n");
    }
  }
  
  MPI_Finalize();
  return 0;
}