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In this paper an algorithm for extracting a stable differential-algebraic subsystem from a path-constrained dynamical system is proposed. The subsystem may be integrated directly by a differential-algebraic system integrator to evaluate constraints in shooting- or multiple shooting- type direct methods for solving path-constrained dynamic optimization problems. The algorithm appends algebraic constraints to the unconstrained ordinary differential equation subsystem based on a stability estimate for the resulting differential-algebraic system. The logarithmic norm is used to compute a stability estimate for index 1 and index 2 subsystems. The working of the algorithm is illustrated with examples. [ABSTRACT FROM AUTHOR]

We discuss two approximation paradigms that were used to construct many approximation algorithms during the last two decades, the primal-dual schema and the local ratio technique. Recently, primal-dual algorithms were devised by first constructing a local ratio algorithm and then transforming it into a primal-dual algorithm. This was done in the case of the $2$-approximation algorithms for the feedback vertex set problem and in the case of the first primal-dual algorithms for maximization problems. Subsequently, the nature of the connection between the two paradigms was posed as an open question by Williamson [Math. Program., 91 (2002), pp. 447--478]. In this paper we answer this question by showing that the two paradigms are equivalent. [ABSTRACT FROM AUTHOR]