anchor.diff:    use datatypes_module
     use grid_module
     use variables_module
  -  use params_module, only : grav, gravity_monopole, hse_vel_type
  +  use params_module, only : grav, gravity_monopole
     use constants_module
   
     implicit none
  
positive.code:         ir = ir + 1
       enddo
          
    case ("hse")
          
       ir = U%grid%lo
       ic = U%grid%lo
               
       do i = U%grid%lo-1, U%grid%lo-U%grid%ng, -1
          ! acceleration depends on hse_vel_type
          select case (hse_vel_type)
          case ("outflow")
             g%data(i,1) = g%data(ic,1)
          case ("reflect")
             g%data(i,1) = -g%data(ir,1)
             ir = ir + 1
          case default
             print *, "ERROR: invalid hse_vel_type"
             stop
          end select
  
       enddo
  
      case ("outflow", "user")
         do i = U%grid%lo-1, U%grid%lo-U%grid%ng, -1
            ! give all quantities a zero-gradient
            g%data(i,1) = g%data(i+1,1)
  
negative.code:           ir = ir - 1
         enddo
  
      case ("outflow", "hse", "user", "diode")
         do i = U%grid%hi+1, U%grid%hi+U%grid%ng
            ! give all quantities a zero-gradient
            g%data(i,1) = g%data(i-1,1)
  