• y1 – (temporarily) uncontrolled output
• y2 – (locally) measured and controlled output (in the inner loop)
We have inserted the word temporarily above, since y1 _ is normally a controlled output at
some higher layer in the hierarchy. We also subdivide the available manipulated inputs in a
similar manner :
• u2 – inputs used for controlling y2 (in the inner loop)
• u1 – remaining inputs (which may be used for controlling y1)