program cartesian

use mpi

implicit none

  INTEGER :: world_rank, row_rank, col_rank, cart_rank
  INTEGER :: nprocs, row_size, col_size
  INTEGER :: dims(2), coords(2)
  LOGICAL :: period(2), sub_coords(2)
  INTEGER :: src_rank, dst_rank
  INTEGER :: sum, temp
  REAL :: avg

  INTEGER :: cart_grid, cart_row, cart_col, status, ierr

  !$ MPI Initialization
  CALL MPI_Init(ierr)
  CALL MPI_Comm_size(MPI_COMM_WORLD, nprocs, ierr)
  CALL MPI_Comm_rank(MPI_COMM_WORLD, world_rank, ierr)

  !$ Cartesian grid creation:
  ! - the function MPI_Dims_create may be used to compute dimensions in both directions
  ! - MPI_Cart_create must be used to create the new topology
  ! - cart_grid will be the handle of the new topology
  dims(1) = 0
  dims(2) = 0
  period(1) = .true.
  period(2) = .true.
	---

  !$ Local world_rank initialization and comparison to global world_rank:
  ! - how can you get 'cart_rank'?
	---
	
  WRITE (*,'(a,i1,a,i1,a)') 'I am world_rank ', world_rank, ' in MPI_COMM_WORLD and world_rank ', cart_rank , ' in the &
  cartesian communicator'

  !$ Coordinates creation and neighbour communication:
  ! - get process cartesian coordinates 'coords' with function MPI_Cart_coords
	---

  !$ Communication south:
  ! - use MPI_Cart_shift and MPI_Sendrecv properly to send local rank to the neighbours
  ! - receive neighbour rank in 'temp' variable and store sum in 'sum'
	---

  !$ Communication north
	---

  !$ Communication east
	---

  !$ Communication west
	---

  !$ Neighbour's average
  avg = REAL(sum)/5
  WRITE (*,'(a,i2,a,i1,a,i1,a,f6.2)') 'Cart rank ', cart_rank, ' (', coords(1), ', ', coords(2), &
       '), neighbours average: ', avg

  !$ Row sub-communicator creation:
  ! - how would you create a "row sub-communicator" ?
  ! - use the function MPI_Cart_sub to get 'cart_row' communicator handle 
  ! - use the proper functions to get 'row_size' and 'row_rank'
   
  sum = 0
  sub_coords(1) = .false.
  sub_coords(2) = .true.
	---

  !$ Use MPI_Reduce to sum up ranks in row sub-communicator
	---

  if (row_rank.eq.0) then
    avg = REAL(sum) /row_size
    WRITE (*,'(a,i1,a,f6.2)') 'Row ',coords(1),' row average: ',avg
  endif

  !$ Column sub-communicator creation:
  ! - repeate to obtain 'cart-col' comm-handle and 'col_size' and 'col_rank'
  sum = 0
  sub_coords(1) = .true.
  sub_coords(2) = .false.
	---

  !$ Use MPI_Reduce to sum up ranks in column sub-communicator's average calculation
	---

  if (col_rank.eq.0) then
    avg = REAL(sum) / col_size
    WRITE (*,'(a,i1,a,f6.2)') 'Column ',coords(2),' column average: ',avg
  endif

  !$ Finalization operations
  CALL MPI_Comm_free(cart_grid, ierr)
  CALL MPI_Comm_free(cart_col, ierr)
  CALL MPI_Comm_free(cart_row, ierr)
  CALL MPI_Finalize(ierr)

end program cartesian