This paper studies a variational obstacle avoidance problem on complete Riemannian manifolds. That is, we minimize an action functional, among a set of admissible curves, which depends on an artificial potential function used to avoid obstacles. In particular, we generalize the theory of bi-Jacobi fields and biconjugate points and present necessary and sufficient conditions for optimality. Local minimizers of the action functional are divided into two categories—called $ Q $-local minimizers and $ \Omega $-local minimizers—and subsequently classified, with local uniqueness results obtained in both cases.
The real (compact) Stiefel manifold realized as set of orthonormal frames is considered as a pseudo-Riemannian submanifold of an open subset of a vector space equipped with a multi-parameter family of pseudo-Riemannian metrics. This family contains several well-known metrics from the literature. Explicit matrix-type formulas for various differential geometric quantities are derived. The orthogonal projections onto tangent spaces are determined. Moreover, by computing the metric spray, the geodesic equation as an explicit second order matrix valued ODE is obtained. In addition, for a multi-parameter subfamily, explicit matrix-type formulas for pseudo-Riemannian gradients and pseudo-Riemannian Hessians are derived. Furthermore, an explicit expression for the second fundamental form and an explicit formula for the Levi-Civita covariant derivative are obtained. Detailed proofs are included.
In this paper we present a unified Lagrangian–Hamiltonian geometric formalism to describe time-dependent contact mechanical systems, based on the one first introduced by K. Kamimura and later formalized by R. Skinner and R. Rusk. This formalism is especially interesting when dealing with systems described by singular Lagrangians, since the second-order condition is recovered from the constraint algorithm. In order to illustrate this formulation, some relevant examples are described in full detail: the Duffing equation, an ascending particle with time-dependent mass and quadratic drag, and a charged particle in a stationary electric field with a time-dependent constraint.
We propose a numerical scheme for the time-integration of nonholonomic mechanical systems, both conservative and nonconservative. The scheme is obtained by simultaneously discretizing the constraint equations and the Herglotz variational principle. We validate the method using numerical simulations and contrast them against the results of standard methods from the literature.
We derive the equations of motion of an action-dependent version of the Einstein-Hilbert Lagrangian, as a specific instance of the Herglotz variational problem. Action-dependent Lagrangians lead to dissipative dynamics, which cannot be obtained with the standard method of Lagrangian field theory. First-order theories of this kind are relatively well understood, but examples of singular or higher-order action-dependent field theories are scarce. This work constitutes an example of such a theory. By casting the problem in clear geometric terms we are able to obtain a Lorentz invariant set of equations, which contrasts with previous attempts.
