1. A method for controlling a nonlinear system, comprising: a linear controller receiving inputs representing measured variables of the system, wherein values of the measured variables of the system are in a first operating region, wherein the linear controller is operable to determine predicted control values for manipulable variables that control the system, and wherein the linear controller has a linear gain k; executing a nonlinear steady-state model of the system, wherein the nonlinear steady-state model has been trained to represent operation of the system over a specified region of the system's operating space, and wherein the nonlinear steady state model has a steady-state gain K; initiating a change in operation of the system, wherein the change operates to move the values of the measured variables of the system from a first operating point to a second operating point, wherein said initiating comprises modifying the nonlinear model in accordance with the change in operation of the system; determining values of the steady-state gain K at the first and second operating points; adjusting the linear gain k of the linear controller as a function of the values of the steady-state gain K of the nonlinear steady-state model at the first and second operating points; the linear controller determining predicted control values for the manipulable variables in response to said adjusting; and outputting the predicted control values for the manipulable variables, wherein the predicted control values are useable to control the system.