/* -----------------------------------------------------------------------
 * Code:   choose.c
 * Lab:    MPI Derived Datatypes
 *         This program sends one single column of a two-dimensional matrix 
 *         from one processor to another.  As currently written, it does this
 *         one column element at a time.  Your task is to modify the program so it 
 *         sends the entire column at once using a derived datatype.  For more 
 *         information on this problem, please read the exercise instructions
 *         that lead you to this code.
 *
 * Usage:  choose
 *         Runs on two nodes.
 * Author: Mike Hammill  Last revised: 2/9/96 MWH
 * ------------------------------------------------------------------------ */

#include "mpi.h"

#define IMAX 15                     /* number of rows in the matrix */
#define JMAX 20                     /* number of columns in the matrix */
#define COL 5                       /* column to send; note: 1 <= COL <= JMAX */
#define COLTAG 10                   /* MPI tag for send and receive */
#define DESTRANK 1                  /* rank of destination process */
#define SOURCERANK 0                /* rank of source process */
#define SPECIAL -1                  /* arbitrary value loaded into the column */
                                    /* to send; used for verification */

main( argc, argv )
     int argc ;
     char **argv ;
{

  int i, j,                        /* index variables */
      myrank;                      /* rank in communicator of process */

  MPI_Status status ;              /* status of received message */
  MPI_Datatype coltype ;           /* derived datatype for you to define */

  double matrix [IMAX][JMAX] ;     /* 2D matrix containing column to send */

  /* Fill matrix with zeros; we do this for later verification of data sent. */

  for ( i=0; i < IMAX; i++ )
    for ( j=0; j < JMAX; j++ )
      matrix[i][j] = 0 ;

  /* Set up MPI environment */

  MPI_Init( &argc, &argv ) ;
  MPI_Comm_rank( MPI_COMM_WORLD, &myrank ) ;
  printf ( "Task %d initialized\n", myrank ) ;

  /* ------------------------------------------------------- */

  if ( myrank == SOURCERANK ) {

    /* In Task with rank of SOURCERANK. */

    /* Fill the column to send, COL, with SPECIAL value. */

    for ( i=0; i < IMAX; i++ )
      matrix[i][COL] = SPECIAL ;

    /* Send the column, one element at a time.  See if   */
    /* you can improve this situation by using a derived */
    /* datatype.                                         */

    for ( i=0; i < IMAX; i++) 
      MPI_Send( &matrix[i][COL], 1, MPI_DOUBLE, DESTRANK, 
	       COLTAG, MPI_COMM_WORLD ) ;
  }

  /* ------------------------------------------------------- */

  else if ( myrank == DESTRANK ) {
    
    /* In Task with rank of DESTRANK. */

    /* Print out matrix before the receive. */

    printf ( "Matrix before receive:\n" ) ;

    for ( i=0; i < IMAX; i++ ) {
      for ( j=0; j < JMAX; j++ ) 
	printf ("%.1f ", matrix[i][j]) ;
      printf ( "\n" ) ;
    }   

    /* Receive the column one element at a time. */
    /* Try to make this a receive of coltype with count=1. */

    for ( i=0; i < IMAX; i++) 
      MPI_Recv( &matrix[i][COL], 1, MPI_DOUBLE, SOURCERANK, 
	       COLTAG, MPI_COMM_WORLD, &status ) ;

    /* Verify the results; print out matrix after receive. */

    printf ( "\nMatrix after receive:\n" ) ; 

    for ( i=0; i < IMAX; i++ ) {
      for ( j=0; j < JMAX; j++ ) 
	printf ("%.1f ", matrix[i][j]) ;
      printf ( "\n" ) ;
    }   

   /* ------------------------------------------------------- */

  }

  MPI_Finalize() ;
}