REASONING ABOUT ENERGY IN QUALITATIVE SIMULATION

Qualitative modeling and simulation make it feasible to predict the possible behaviors of a mechanism consistent with an incomplete state of knowledge. Though qualitative simulation predicts all possible behaviors of a system, it can also produce spurious behaviors, i.e., behaviors that correspond to no solution of any ordinary differential equation consistent with the qualitative model. A method for reasoning about energy is presented that eliminates an important source of spurious behaviors. This method is applied to an industrially significant mechanism-a nonlinear, proportional-integral controller-and show that qualitative simulation captures the main qualitative properties of such a system, such as stability and zero-offset control. It is believed that this is a significant step toward the application of qualitative simulation to model-based monitoring, diagnosis, and design of realistic mechanisms.