//
// 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 <iostream>
#include <mpi.h>

using namespace std;

 
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, lowerbound;
  
  MPI::Init (argc, argv);
  myrank = MPI::COMM_WORLD.Get_rank();
  size = MPI::COMM_WORLD.Get_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)
	cout << a[i][j] << " ";
      cout << endl;
    }
  }
  
  // Create a submatrix datatype

  MPI::INT.Get_extent(lowerbound, sizeofint);
  
  // Create datatype for the sub-row

  subrow = MPI::INT.Create_vector(5, 1, 2);

  // Commit the datatype created

  subrow.Commit();
  
  // Create datatype for the sub-matrix

  submatrix = subrow.Create_hvector(5, 1, 20*sizeofint);
  
  // Commit the datatype created

  submatrix.Commit();
  
  // Send it to self and print it

  MPI::COMM_WORLD.Sendrecv(a, 1, submatrix, myrank, 0, c, 5 * 5, MPI::INT,
			   myrank, 0);
  
  // Print the submatrix

  if (myrank == 0) {
    for (i = 0; i < 5; ++i) {
      for (j = 0; j < 5; ++j)
	cout << c[i][j] << " ";
      cout << endl;
    }
  }
  
  MPI::Finalize();
  return 0;
}