1. A non-transitory memory medium comprising program instructions executable by a processor, wherein the program instructions comprise: a non-linear model comprising an empirical representation of a plant or process, wherein the non-linear model is configured to receive an input value from the plant or process, and to generate a first output value using the empirical representation of the plant or process; and a linearized first principles model comprising an analytic representation of the plant or process, wherein the linearized first principles model is configured to receive the input value from the plant or process, and to generate a second output value using the analytic representation of the plant or process.