Qualitative simulation is a useful method for predicting the possible qualitatively distinct behaviors of an incompletely known mechanism described by a system of qualitative differential equations (QDEs). Under some circumstances, sparse information about the derivatives of variables can lead to intractable branching (or "chatter") representing uninteresting or even spurious distinctions among qualitative behaviors. The problem of chatter stands in the way of real applications such as qualitative simulation of models in the design or diagnosis of engineered systems. One solution to this problem is to exploit information about higherorder derivatives of the variables. We demonstrate automatic methods for identification of chattering variables, algebraic derivation of expressions for second-order derivatives, and evaluation and application of the sign of second- and third-order derivatives of variables, resulting in tractable simulation of important qualitative models. Caution is requir...

Qualitative Modeling and Interpretation (QMI) and Qmimic are on-line monitoring and diagnosis systems which use multiple qualitative models of a plant to monitor noisy data streams and rapidly diagnose faults from observed dynamic behavior. Both systems continue monitoring after faults have occurred. QMI simulates normal and faulty plant behavior off-line using purely qualitative Qsim models, and uses plant data to select the correct model, yielding a diagnosis. Qmimic incrementally simulates on-line qualitative models which describe the current behavior of the plant, using plant data to constrain further prediction and select between the models. Although both systems are based on qualitative models of the plant, Qmimic also incorporates semi-quantitative data (quantitative ranges and bounding envelopes) into the qualitative simulation in order to achieve better predictions. QMI and Qmimic are described and compared in detail, and both are tested on a simulated chemical reactor. 1 Intr...