anchor.diff:  
       ! Translate debug_c (zero-based verbosity indicator) approximately
       ! to print_control (general signed integer with meaning attached to
  -    ! certain values)
  +    ! certain values).  TODO consider debug vs. print_control.
       print_control = debug_c - 1
   
       ! Initialize the state and task
  
positive.code:      ! 'status_message_length': Usable length of 'status_message_c'
       !    buffer.  Recommend at least 100.
       !
       ! 'status_message': Returns a message explaining the exit status.
       !
       ! 'status': Returns the exit status code, one of the
       !    LBFGSB_STATUS_* constants defined in enumeration above.
  
negative.code:   ! 'status_message_length_c': Usable length of 'status_message_c'
    !    buffer.  Recommend at least 100.
    !
    ! 'status_message_c': Message (null-terminated C string) explaining
    !    the exit status.
    !
    ! 'debug_c': Output verbosity level where 0 means no output and larger
    !    values mean increasing output.
  