Theorem 6 (Structure-preserving integrators) Lie group variational integrators constructed via discrete variational principles on G (e.g., discrete Lagrangian on SE(3)) produce discrete flows that preserve group structure and a discrete momentum map; they exhibit good long-term energy behavior. Convergence and order results are stated and proven for schemes of practical interest (Section 9).
Theorem 2 (Euler–Lagrange on manifolds) Let Q be a smooth configuration manifold and L: TQ → R a C^2 Lagrangian. A C^2 curve q(t) is an extremal of the action integral S[q] = ∫ L(q, q̇) dt with fixed endpoints iff it satisfies the Euler–Lagrange equations in local coordinates; coordinate-free formulation uses the variational derivative dS = 0 leading to intrinsic equations. (Proof: Section 4, including existence/uniqueness under regularity assumptions.) rigid dynamics krishna series pdf
Abstract A self-contained, rigorous treatment of rigid-body dynamics is presented, unifying classical formulations (Newton–Euler, Lagrange, Hamilton) with modern geometric mechanics (Lie groups, momentum maps, reduction, symplectic structure). The monograph develops kinematics, equations of motion, variational principles, constraints, stability and conservation laws, and computational techniques for simulation and control. Emphasis is placed on mathematical rigor: precise definitions, well-posedness results, coordinate-free formulations on SE(3) and SO(3), and proofs of equivalence between formulations. A C^2 curve q(t) is an extremal of