anchor.diff:       real :: dt
        real :: t
        real :: t_end
  +
  +     real :: alpha
   
        integer :: n_x
        integer :: n_y
  
positive.code:     write(*,"(a10, i8)") "n_y:", model%n_y
      write(*,"(a10, f8.2)") "dx:", model%dx
      write(*,"(a10, f8.2)") "dy:", model%dy
      write(*,"(a10, f8.2)") "dt:", model%dt
      write(*,"(a10, f8.2)") "t:", model%t
      write(*,"(a10, f8.2)") "t_end:", model%t_end
  
negative.code:   subroutine initialize_from_defaults(model)
      type (heat_model), intent (out) :: model
  
      model%alpha = 1.0
      model%t_end = 20.
      model%n_x = 10
      model%n_y = 20
  