Summary.The two most popular formulations of the equations of constrained mechanical motion, the descriptor and state-space forms, each have severe practical limitations. In this paper, we discuss and relate some proposed reformulations of the equations which have improved numerical properties.
Subject classifications. AMS(MOS): 65L05; CR: G1.7
I IntroductionWe are concerned with the equations of constrained mechanical motion. The equations are typically developed from variational principles, and the resulting system, which can be considered a differential equation on a manifold, is mapped to an ordinary differential equation [2]. The mapping is not easily automated, nor necessarily desirable in the computational setting, while the original constrained statement of the problem is not solvable by current numerical software.Two alternative formulations have recently been discussed in the literature, one based on an overdetermined system of equations including time derivatives of the constraints, and the other based on stabilization with respect to those differentiated constraints via additional Lagrange multipliers. These formulations lead to systems of equations which are more amenable to numerical computation than either of the two traditional models. In the sequel we discuss and relate the reformulations, in the context of numerical discretization.Historically, mechanical systems have been formulated as Lagrange equations of the first or second kind. The Lagrangian equations of the first kind, derived directly from variational principles, are a constrained differential equation or a differential-algebraic equation (DAE): Offprint requests to: C. Fiihrer