The distillation column shown in the drawing is used to distill a binary mixture. symbols x, y, and z denote mole frac- tions of the more volatile component, while b, d, r, and f represent molar flow rates. it is desired to control distillate composition y despite disturbances in feed flow rate f. all flow rates can be measured and manipulated with the excep- tion of f, which can only be measured. a composition ana- lyzer provides measurements of y.