1. A method, comprising: providing a model, wherein the model comprises a representation of a plant or process, wherein the model comprises one or more inputs and one or more outputs, wherein the model comprises one or more gains, and wherein each gain comprises a respective partial derivative of an output with respect to a respective input; specifying one or more user-configurable gain constraints, wherein each of the one or more user-configurable gain constraints corresponds to a respective gain; and training the model with a non-linear programming optimizer subject to the one or more user-configurable gain constraints.