cart.C

#include <stdio.h>
#include <mpi.h>
 
#define NDIMS   2
 
typedef enum { NORTH, SOUTH, EAST, WEST } Direction;
 
// A node in 2-D torus
class Node {
private:
  MPI_Comm      comm;
  int           dims[NDIMS], coords[NDIMS];
  int           grank, lrank;
  int           data;
public:
  Node(void);
  ~Node(void);
  void profile(void);
  void print(void);
  void shift(Direction);
};
 
// A constructor
Node::Node(void)
{
  int i, nnodes, periods[NDIMS];
 
  // Create a balanced distribution
  MPI_Comm_size(MPI_COMM_WORLD, &nnodes);
  for (i = 0; i < NDIMS; i++) { dims[i] = 0; }
  MPI_Dims_create(nnodes, NDIMS, dims);
 
  // Establish a cartesian topology communicator
  for (i = 0; i < NDIMS; i++) { periods[i] = 1; }
  MPI_Cart_create(MPI_COMM_WORLD, NDIMS, dims, periods, 1, &comm);
 
 // Initialize the data
  MPI_Comm_rank(MPI_COMM_WORLD, &grank);
  if (comm == MPI_COMM_NULL) {
    lrank = MPI_PROC_NULL;
    data = -1;
  } else {
    MPI_Comm_rank(comm, &lrank);
    data = lrank;
    MPI_Cart_coords(comm, lrank, NDIMS, coords);
  }
}
 
// A destructor
Node::~Node(void)
{
  if (comm != MPI_COMM_NULL) {
    MPI_Comm_free(&comm);
  }
}
 
// Shift function
void Node::shift(Direction dir)
{
  if (comm == MPI_COMM_NULL) { return; }
 
  int direction, disp, src, dest;
 
  if (dir == NORTH) {
    direction = 0; disp = -1;
  } else if (dir == SOUTH) {
    direction = 0; disp = 1;
  } else if (dir == EAST) {
    direction = 1; disp = 1;
  } else {
    direction = 1; disp = -1;
  }
  MPI_Cart_shift(comm, direction, disp, &src, &dest);
  MPI_Status stat;
  MPI_Sendrecv_replace(&data, 1, MPI_INT, dest, 0, src, 0, comm, &stat);
}
// Synchronize and print the data being held
 
void Node::print(void)
{
  if (comm != MPI_COMM_NULL) {
    MPI_Barrier(comm);
    if (lrank == 0) { puts(""); } // line feed
    MPI_Barrier(comm);
    printf("(%d, %d) holds %d\n", coords[0], coords[1], data);
  }
}
 
// Print object's profile
void Node::profile(void)
{
  // Non-member does nothing
  if (comm == MPI_COMM_NULL) { return; }
 
  // Print "Dimensions" at first
  if (lrank == 0) {
    printf("Dimensions: (%d, %d)\n", dims[0], dims[1]);
  }
  MPI_Barrier(comm);
 
  // Each process prints its profile
  printf("global rank %d: cartesian rank %d, coordinate (%d, %d)\n",
         grank, lrank, coords[0], coords[1]);
}
 
// Program body
//
// Define a torus topology and demonstrate shift operations.
//
 
void body(void)
{
  Node node;
 
  node.profile();
 
  node.print();
 
  node.shift(NORTH);
  node.print();
  node.shift(EAST);
  node.print();
  node.shift(SOUTH);
  node.print();
  node.shift(WEST);
  node.print();
}
//
// Main program---it is probably a good programming practice to call
//   MPI_Init() and MPI_Finalize() here.
//
int main(int argc, char **argv)
{
  MPI_Init(&argc, &argv);
  body();
  MPI_Finalize();
}