/* -----------------------------------------------------------------------
 * Code:   to.complete.c
 * Lab:    MPI Derived Datatypes
 *         This program sends contiguous data of mixed type (a C struct)
 *         from one process to another.  You have to initialize the values
 *         for the parameters to the MPI_Type_struct call, and properly 
 *         insert them.
 *
 * Usage:  to.complete
 *         Runs on two nodes.
 * Author: Mike Hammill  Last revised: 2/9/96 MWH
 * ------------------------------------------------------------------------ */

#include "mpi.h"

#define PACKET_BLOCKS 2    /* number of elements in struct */
#define FMAX 14            /* length of array of forces */
#define PACKETTAG 99       /* MPI tag for packet to be sent and received */
#define DESTRANK 1         /* rank of destination process */
#define SOURCERANK 0       /* rank of source process */
#define MYMASS 150.0       /* arbitrary constant */

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

  /* -------------------------------------------------------------- */
  /* You fill in the blocklengths */
  /* -------------------------------------------------------------- */
  int array_of_blocklengths[PACKET_BLOCKS] 
    = {, },                                 /* for MPI struct */
    i,                                      /* loop index */
    myrank ;                                /* rank in communicator of process */

  MPI_Aint extent,                          /* extent of double */
    array_of_displacements[PACKET_BLOCKS] ; /* for MPI struct */

  MPI_Datatype 

    /* -------------------------------------------------------------- */
    /* You fill in the array_of_types */
    /* -------------------------------------------------------------- */
    array_of_types[PACKET_BLOCKS] 
      = {, },                               /* for MPI struct */
    packettype ;

  MPI_Status status ;                       /* status of received message */

  /* We want to send packet, a contiguous C struct with mixed types. */
  /* Declare packet prior to constructing a new derived datatype. */

  struct{
    double mass ;                           /* an object's mass */
    int force[FMAX] ;                       /* array of forces */
  } packet ;

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

  /* Initialize packet to zero. */

  packet.mass = 0.0 ;

  for (i=0; i < FMAX; i++)
         packet.force[i] = 0.0 ;

  /* Setup the MPI environment. */

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

  /* Note that all the following variables are constants */
  /* and depend only on the format of the C struct. */

  /* -------------------------------------------------------------- */
  /* You fill in the values for displacements */
  /* -------------------------------------------------------------- */

  array_of_displacements[0] =  ; 
  array_of_displacements[1] =  ; 

  /* Use these variables to create a new derived datatype and commit. */

  /* -------------------------------------------------------------- */
  /* You fill in arguments to the MPI_Type_struct call. */
  /* -------------------------------------------------------------- */
  MPI_Type_struct (, , , , ) ;

  MPI_Type_commit (&packettype) ;

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

  if ( myrank == SOURCERANK ) {

    /* Give packet values so we can verify they get sent. */

    packet.mass = MYMASS ;

    for (i=0; i < FMAX; i++)
      packet.force[i] = (i+1) * 100 ;

    /* Send packettype with count=1. */

    MPI_Send( &packet, 1, packettype, DESTRANK, 
	     PACKETTAG, MPI_COMM_WORLD ) ;
  }

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

  else if ( myrank == DESTRANK ) {

    /* Task with DESTRANK will receive packettype with count=1 */

    /* Print packet before the receive. */

    printf ("Value of packet before receive:\n") ;
    printf ("Mass =  %.3f \n", packet.mass) ;
    printf ("Array of forces = " ) ; 
    for ( i=0; i < FMAX; i++ ) 
      printf ("%d  ", packet.force[i] ) ; 
    printf ( "\n" ) ; 

    MPI_Recv( &packet, 1, packettype, SOURCERANK, 
	     PACKETTAG, MPI_COMM_WORLD, status ) ;

    /* Verify that structure got passed. */

    /* Print packet before the receive. */

    printf ("\nValue of packet after receive:\n") ;
    printf ("Mass =  %.3f \n", packet.mass) ;
    printf ("Array of forces = " ) ; 
    for ( i=0; i < FMAX; i++ ) 
      printf ("%d  ", packet.force[i] ) ; 
    printf ( "\n" ) ; 

  }

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

    MPI_Finalize() ;
}