This paper proves two main results. First, it is shown that if Σ is a smooth manifold homeomorphic to the standard n-torus T n = R n Z n and H is a real-analytically completely integrable convex hamiltonian on T ∗Σ, then Σ is diffeomorphic to Tn. Second, it is proven that for some topological 7-manifolds, the cotangent bundle of each smooth structure admits a real-analytically completely integrable riemannian metric hamiltonian.
@cite_1 , Rudnev and Ten assume that a geodesic flow is completely integrable with a non-degenerate first-integral map on an @math -dimensional compact manifold with first Betti number equal to @math . Non-degeneracy means, amongst other things, that the singular set is stratified by the rank of the first integral map and each stratum is a symplectic submanifold on which the system is completely integrable. From these hypotheses, they deduce that there is a lagrangian torus @math such that the natural map @math (figure ) is a homeomorphism . Theorem 2 of @cite_1 states that @math is a diffeomorphism, but this is mistaken. It is shown only that @math is a @math smooth map, hence by invariance of domain, a homeomorphism. To prove that @math is a diffeomorphism one must prove that the Maslov cocycle of @math vanishes, or something equivalent. This is the first difficulty in proving theorem .
@cite_1
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This study derives geometric, variational discretization of continuum theories arising in fluid dynamics, magnetohydrodynamics (MHD), and the dynamics of complex fluids. A central role in these discretizations is played by the geometric formulation of fluid dynamics, which views solutions to the governing equations for perfect fluid flow as geodesics on the group of volume-preserving diffeomorphisms of the fluid domain. Inspired by this framework, we construct a finite-dimensional approximation to the diffeomorphism group and its Lie algebra, thereby permitting a variational temporal discretization of geodesics on the spatially discretized diffeomorphism group. The extension to MHD and complex fluid flow is then made through an appeal to the theory of Euler–Poincare systems with advection, which provides a generalization of the variational formulation of ideal fluid flow to fluids with one or more advected parameters. Upon deriving a family of structured integrators for these systems, we test their performance via a numerical implementation of the update schemes on a cartesian grid. Among the hallmarks of these new numerical methods are exact preservation of momenta arising from symmetries, automatic satisfaction of solenoidal constraints on vector fields, good long-term energy behavior, robustness with respect to the spatial and temporal resolution of the discretization, and applicability to irregular meshes.