More Like this

1. Identifiability and Observability of Nonsmooth Systems via Taylor-Like Approximations

   https://doi.org/10.1109/TAC.2025.3533366  

   Stechlinski, Peter; Eisa, Sameh A; Abdelfattah, Hesham (January 2025, IEEE Transactions on Automatic Control)

   New sensitivity-based methods are developed for determining identifiability and observability of nonsmooth input-output systems. More specifically, lexicographic derivatives are used to construct nonsmooth sensitivity rank condition (SERC) tests, which we call lexicographic SERC (L-SERC) tests. The introduced L-SERC tests are practically implementable, accurate, and analogous to (and indeed recover) their smooth counterparts. To accomplish this, a novel first-order Taylor-like approximation theory is developed to directly treat nonsmooth (i.e., continuous but nondifferentiable) functions. An L-SERC algorithm is proposed that determines partial structural identifiability or observability, which are useful characterizations in the nonsmooth setting. Lastly, the theory is illustrated through an application in climate modeling. 

   more » « less
2. Parameter Identifiability and Reduction for Smooth and Nonsmooth Differential-Algebraic Equation Systems

   https://doi.org/10.1109/LCSYS.2024.3521427  

   Abdelfattah, Hesham; Stechlinski, Peter; Eisa, Sameh A (December 2024, IEEE Control Systems Letters)

   We extend the sensitivity rank condition (SERC), which tests for identifiability of smooth input-output systems, to a broader class of systems. Particularly, we build on our recently developed lexicographic SERC (L-SERC) theory and methods to achieve an identifiability test for differential-algebraic equation (DAE) systems for the first time, including nonsmooth systems. Additionally, we develop a method to determine the identifiable and non-identifiable parameter sets. We show how this new theory can be used to establish a (non-local) parameter reduction procedure and we show how parameter estimation problems can be solved. We apply the new methods to problems in wind turbine power systems and glucose-insulin kinetics. 

   more » « less
3. Sensitivity and Optimal Control Theory for Linear Complementarity Systems

   https://doi.org/10.1007/978-3-031-84869-8_44  

   Stechlinski, Peter; Abdelfattah, Hesham; Eisa, Sameh A (January 2025, Springer Nature Switzerland)

   Kilgour, D_M; Kunze, H; Makarov, R_N; Melnik, R; Wang, X (Ed.)

   This article focuses on sensitivity and control theory for linear complementarity systems (LCSs), a type of dynamical system that experiences hybrid continuous/discrete behavior and is therefore nonsmooth. In particular, a sensitivity theory is given that characterizes generalized derivative information of solutions of LCSs with respect to parametric perturbations. With this theory in hand, a computationally-relevant open-loop optimal control theory is provided using a direct method (i.e., the control is parametrically discretized and generalized gradients of the objective function are described). The approach here is based on lexicographic directional differentiation theory, a relatively new tool in nonsmooth analysis, being applied to nonlinear complementarity systems (NCSs). The optimal control theory is illustrated with an example. As a byproduct of the sensitivity theory, well-posedness results for a new class of hybrid dynamical system, called the lexicographic linear complementarity system (LexLCS), are also established. 

   more » « less
4. Observability analysis and state estimation of wind turbine power systems: A novel sensitivity-based approach

   https://doi.org/10.1016/j.ifacsc.2026.100370  

   Abdelfattah, Hesham; Eisa, Sameh A; Stechlinski, Peter (March 2026, IFAC Journal of Systems and Control)

   In this paper, we provide a novel framework that enables a sensitivity-based observability test and state estimation algorithm for wind turbine power systems (WTPSs). The provided framework is the first of its kind in the literature, as it is able to deal with state-of-the-art WTPS models that are non-reduced, highly nonlinear differential–algebraic equation systems. Moreover, the framework includes nonsmoothness in both the dynamics and output functions to unify the operational conditions over different wind speed regions. We demonstrate the effectiveness of the proposed framework (thanks to the underlying tools from generalized derivatives theory) on different wind speed profiles, including real-world wind data. We also illustrate how the proposed framework, by the utilization of robust observability analysis during nonsmooth transitions, enables accurate state estimation for cases when the conventional Extended Kalman Filter approach fails. 

   more » « less
5. Ensuring the Observability of Structural Test Obligations

   https://doi.org/10.1109/TSE.2018.2869146  

   Meng, Ying; Gay, Gregory; Whalen, Michael (September 2018, IEEE Transactions on Software Engineering)

   Test adequacy criteria are widely used to guide test creation. However, many of these criteria are sensitive to statement structure or the choice of test oracle. This is because such criteria ensure that execution reaches the element of interest, but impose no constraints on the execution path after this point. We are not guaranteed to observe a failure just because a fault is triggered. To address this issue, we have proposed the concept of observability—an extension to coverage criteria based on Boolean expressions that combines the obligations of a host criterion with an additional path condition that increases the likelihood that a fault encountered will propagate to a monitored variable. Our study, conducted over five industrial systems and an additional forty open-source systems, has revealed that adding observability tends to improve efficacy over satisfaction of the traditional criteria, with average improvements of 125.98% in mutation detection with the common output-only test oracle and per-model improvements of up to 1760.52%. Ultimately, there is merit to our hypothesis—observability reduces sensitivity to the choice of oracle and to the program structure. 

   more » « less