1. A model predictive control process for controlling a physical process through actuators that have a polytopic defined constraint set defining the operational limitations of the actuators, the process comprising: periodically sampling one or more sensors whose outputs characterize operational results of the physical process; computing a desired set of manipulated variables, by conducting an off-line computation which approximates the constraint set as an ellipsoid; conducting an on-line scaling to scale the ellipsoid approximation to the constraint set and implement a selected control algorithm; and adjusting the actuators according to the scaling.