mg_prolong_buffer_size Subroutine

  subroutine mg_prolong_buffer_size(mg, n_send, n_recv, dsize)
    type(mg_t), intent(inout) :: mg
    integer, intent(out)      :: n_send(0:mg%n_cpu-1)
    integer, intent(out)      :: n_recv(0:mg%n_cpu-1)
    integer, intent(out)      :: dsize
    integer                   :: lvl, min_lvl

    if (.not. allocated(mg%comm_restrict%n_send)) then
       error stop "Call restrict_buffer_size before prolong_buffer_size"
    end if

    min_lvl = max(mg%first_normal_lvl-1, mg%lowest_lvl)
    allocate(mg%comm_prolong%n_send(0:mg%n_cpu-1, min_lvl:mg%highest_lvl))
    allocate(mg%comm_prolong%n_recv(0:mg%n_cpu-1, min_lvl:mg%highest_lvl))

    mg%comm_prolong%n_recv(:, mg%highest_lvl) = 0
    mg%comm_prolong%n_send(:, mg%highest_lvl) = 0

    do lvl = min_lvl, mg%highest_lvl-1
       mg%comm_prolong%n_recv(:, lvl) = mg%comm_restrict%n_send(:, lvl+1)
       mg%comm_prolong%n_send(:, lvl) = mg%comm_restrict%n_recv(:, lvl+1)
    end do

    ! Send fine grid points, because this is more flexible than sending coarse
    ! grid points (e.g., when multiple variables are used for interpolation)
    dsize = (mg%box_size)**2
    n_send = maxval(mg%comm_prolong%n_send, dim=2)
    n_recv = maxval(mg%comm_prolong%n_recv, dim=2)
  end subroutine mg_prolong_buffer_size