anchor.diff:      if (.not. sane) then
          error_msg = "Virtual detectors must be present in numerical grid; "// &
               "stopping abnormally."
  -       write(*,*) nxl_vd, nxr_vd
          call log_log_critical(error_msg, log_stderr)
          stop 0
       end if
  
positive.code:     this%p_min = p_min
      this%p_max = p_max
  
      write(*,*) p_min, p_max
  
      this%dt = dt
  
      this%semi_classical = sc
  
negative.code:     logical :: sane
      character(:), allocatable :: error_msg
  
      sane = (nxl_ext .gt. 0) .and. (nxr_ext .gt. 0)
      if (.not. sane) then
         error_msg = "No external region defined in numerical grid; "// &
  