Where L is much greater than 1, a minimum gain constraint on inv(S) (green shaded
region) is equivalent to a minimum gain constraint on L. Similarly, where L is much
smaller than 1, a maximum gain constraint on T (red shaded region) is equivalent to a
maximum gain constraint on L. The gap between these two constraints is twice the
crossover tolerance, which specifies the frequency band where the loop gain can cross 0
dB.
For multi-input, multi-output (MIMO) control systems, values in the gain profile greater
than 1 are interpreted as minimum performance requirements. Such values are lower
Loop Shape Goal