Interaction index for multivariable control systems

An interaction index is defined for a linear time-invariant multivariable control system which gives a measure of the degree of interaction which will occur when two or more linear time-invariant proportional-feedback control systems are applied simultaneously to the system. The index is simple to compute, and so should be useful in predicting when interaction will occur in large multivariable control systems. A numerical example of a distillation column with pressure control and temperature control is included.