Generalised Nyquist self-tuning control: a going concern?

The characteristic decomposition of a plant model defines a set of SISO decoupled subsystems whose behaviour bears a strong correlation to the model´s individual loop behaviour. Thus, to self-tune a MIMO system one must self-tune the characteristic subsystem; and this can be done using any SISO self-tuning techniques. In the first instance, for an efficient application of the multivariable algorithm, one would require the plant poles and branch points to be stable. It is the purpose of this paper to remove these restrictions and extend the efficacy of the technique