Implicit Method for Degenerated Differential-Algebraic Equations and Applications

Systems of differential-algebraic equations are routinely automatically produced by modeling enviroments such as Maplesim, System Modeler and Modelica. Structural methods are important for reducing the index and obtaining hidden constraints of such daes. This is especially the case for high index non-linear daes. Although such structural analysis is often successful for many dynamic systems, it may fail if the resulting Jacobian is still singular due to symbolic cancellation or numerical degeneration. Existing modified structural methods can handle some cases caused by symbolic cancellation, where assumes the determinant of a Jacobian matrix is identically zero. This paper removes such assumptions and provides numerical methods to analyze such degenerated cases using real algebraic geometry for polynomially nonlinear daes. Firstly, we provide a witness point method, which produces witness points on all components and can help to detect degeneration on all components of polynomially daes. Secondly, we propose an implicit index reduction method which can restore a full rank Jacobian matrix for degenerated dae. Thirdly, based on IIR, we introduce an improved structural method, which can numerically solve degenerated daes on all components. Examples are given to illustrate our methods and show their advantages for degenerated daes.