How statement and proof provenance work
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The point transformation of the model: the chart transition is generated in the second kind, has a nowhere invertible -projection, and is contrasted with the momentum shift
A worked projection and generating-function computation for the declared potential presentation: a genuine chart of the configuration domain induces the momentum chart transition from generalized momentum to Cartesian momentum , , generated in the second kind by the action-dimensioned function ; the transition has unit determinant and fails the first-kind projection hypothesis identically. The degenerate case is compared with the momentum shift, whose second-kind generating function is global. All quantities are model values of the declared idealization; no measurement is reported.
Example
Declare the one-label model of the force branch Adopted force model: force maps, the equation of motion, additive composition of force contributions and frame covariance with , mass , configuration domain , a potential and no residual forces, and let be a generalized-coordinate chart of the configuration domain: , of class , invertible for every (Generalized-coordinate maps of the model, the substituted Lagrangian, the kinetic metric and generalized forces, Configuration domain of labeled particles: open admissible sets, regular holonomic constraints and the mass operator, Potential presentations of a force model, potential and mechanical energy, closed versus exact force fields, local potentials and equipotential level sets, The action functional of a force model with a potential presentation: the mechanical Lagrangian, its chart instance and its dimensions). Let the generalized coordinates have declared dimensions ; their conjugate generalized momenta have dimensions . The Cartesian positions have dimension and their conjugate Cartesian momenta have dimension , by Dimensions and SI unit conventions of the non-relativistic classical mechanics framework and Generalized-coordinate maps of the model, the substituted Lagrangian, the kinetic metric and generalized forces. The induced momentum chart transition of the presentation is
the second equality because when is invertible and (The canonical one-form and the two-form of a potential presentation: on the Cartesian momentum phase chart and the induced forms on each generalized-coordinate chart, The momentum of a potential presentation: the fibre derivative of the mechanical Lagrangian, the Cartesian momentum Mv and generalized momenta, Hyperregular potential presentations and their inverse Legendre branches in the model's charts). Then:
- the function on is of class and has action dimension ; its mixed derivative matrix is , whose determinant is nonzero. Here is the new Cartesian momentum, while is the old generalized momentum. The second-kind relations are and , so solving for gives , exactly ; consequently is a canonical map of the presentation with (Generating functions of the first and second kind for a local canonical map, The local map generated by a first- or second-kind generating function is a canonical local diffeomorphism);
- determinant check: with the block decomposition in source coordinates and target coordinates the derivative is block triangular,
- the -projection is independent of the momentum and has derivative of rank at every point: it is nowhere invertible. Since a first-kind generating function requires the relation to be solvable for , i.e. the map to be a local diffeomorphism, the transition admits no first-kind generating function near any point; the second-kind representation of claim 1 is the available local description (Generating functions of the first and second kind for a local canonical map, A canonical map with invertible -projection is locally generated by a first-kind generating function);
- contrast — the Cartesian momentum shift: for a constant of momentum dimension the map of the Cartesian chart is canonical trivially (), its first-kind projection is degenerate identically, and it has the global second-kind generating function , also of action dimension, since and (Generating functions for a potential presentation: first- and second-kind data generate canonical maps locally, the local converse under an invertible projection, and the time-dependent Hamiltonian clause 2).
All quantities are model values of the declared idealization; no measurement is reported.
Facts & Assumptions
Given: The one-label model with a genuine chart of the configuration domain, the induced momentum chart transition , and the generating-function data of the two examples.
Chart data and units (Generalized-coordinate maps of the model, the substituted Lagrangian, the kinetic metric and generalized forces, The momentum of a potential presentation: the fibre derivative of the mechanical Lagrangian, the Cartesian momentum Mv and generalized momenta, Hyperregular potential presentations and their inverse Legendre branches in the model's charts, Every potential presentation is hyperregular in its charts, with inverse branch (or ) and the explicit kinetic-plus-potential Hamiltonian, The canonical one-form and the two-form of a potential presentation: on the Cartesian momentum phase chart and the induced forms on each generalized-coordinate chart, The two-form of a potential presentation is closed and nondegenerate, and each generalized-coordinate momentum chart carries the same symplectic structure: and , Configuration domain of labeled particles: open admissible sets, regular holonomic constraints and the mass operator, Dimensions and SI unit conventions of the non-relativistic classical mechanics framework): is a immersion with invertible, , the generalized momentum is with , and the transition is , whose output is Cartesian momentum of dimension .
Generating functions and their canonical maps (Generating functions of the first and second kind for a local canonical map, The local map generated by a first- or second-kind generating function is a canonical local diffeomorphism, A canonical map with invertible -projection is locally generated by a first-kind generating function, The Euclidean inverse function theorem): a second-kind datum with generates a canonical local diffeomorphism via old generalized momentum and new Cartesian position , with unit determinant; a first-kind datum requires , so is a local diffeomorphism. The generating functions have action dimension. For the point transformation the mathematical proposition applies with and , using the standard source and target forms supplied by [F1]; the Cartesian-domain theorem Generating functions for a potential presentation: first- and second-kind data generate canonical maps locally, the local converse under an invertible projection, and the time-dependent Hamiltonian clause 2 applies to the momentum shift with .
Calculus and matrix algebra ( Euclidean maps and diffeomorphisms, The Jacobian matrix of partial derivatives and the gradient in the scalar-valued case, Directional derivatives and partial derivatives of a map , Rectangular matrix multiplication and the identity matrix , including zero-sized shapes, The transpose of a matrix, Linear map between vector spaces over the same field, Invertible matrices and the general linear group , A positive-sized square matrix over a commutative ring is invertible if and only if its determinant is a unit, For , the determinant over a commutative ring by the Leibniz formula, and for a real matrix, Submersions and immersions between Euclidean open sets): has generalized-momentum components , so has action dimension; the displayed partial derivatives are computed by the ordinary rules, transposes and inverses obey , and a matrix with a vanishing block column has rank at most the number of its nonzero columns.
Verification
Second-kind generation: by [F3], and , so has nonzero determinant by [F1]. The generated relations of [F2] are and , i.e. and : this is , canonical with unit determinant and with ; claim 1.
Momentum shift: for the derivative is the identity, so and the map is canonical; with one has and , so [F2] gives , , i.e. , with ; the first-kind projection is constant in and hence degenerate; this is claim 4.
Determinant check: in the coordinates on the source and on the target, the derivative of is the displayed block-triangular matrix with diagonal blocks and ; because and , its determinant is , which is claim 2.
Projection obstruction: the -projection of sends to , with derivative the displayed block matrix whose second block column vanishes; its rank is at most , so it is nowhere invertible. By [F2], a first-kind generating function would make a local diffeomorphism whose inverse is exactly this projection, which is impossible; hence no first-kind generating function exists near any point, proving claim 3.
Collecting steps 1.1, 2.1, 2.2 and 1.2 proves the four claims on the declared data.
Depends on
The canonical one-form and the two-form of a potential presentation: on the Cartesian momentum phase chart and the induced forms on each generalized-coordinate chart
The two-form of a potential presentation is closed and nondegenerate, and each generalized-coordinate momentum chart carries the same symplectic structure: and
Canonical coordinates and the canonical form of the two-form for a potential presentation: the coordinate expression with the chart's half-dimension, and the model's own momentum charts
Canonical maps of a potential presentation: pullback-preserving immersions and the equal-dimensional determinant and field-transport tests
Generating functions for a potential presentation: first- and second-kind data generate canonical maps locally, the local converse under an invertible projection, and the time-dependent Hamiltonian
Generating functions of the first and second kind for a local canonical map
The local map generated by a first- or second-kind generating function is a canonical local diffeomorphism
A canonical map with invertible -projection is locally generated by a first-kind generating function
Generalized-coordinate maps of the model, the substituted Lagrangian, the kinetic metric and generalized forces
The momentum of a potential presentation: the fibre derivative of the mechanical Lagrangian, the Cartesian momentum Mv and generalized momenta
Hyperregular potential presentations and their inverse Legendre branches in the model's charts
Every potential presentation is hyperregular in its charts, with inverse branch (or ) and the explicit kinetic-plus-potential Hamiltonian
The action functional of a force model with a potential presentation: the mechanical Lagrangian, its chart instance and its dimensions
Potential presentations of a force model, potential and mechanical energy, closed versus exact force fields, local potentials and equipotential level sets
Adopted force model: force maps, the equation of motion, additive composition of force contributions and frame covariance
Configuration domain of labeled particles: open admissible sets, regular holonomic constraints and the mass operator
Dimensions and SI unit conventions of the non-relativistic classical mechanics framework
The Euclidean inverse function theorem
Euclidean maps and diffeomorphisms
The Jacobian matrix of partial derivatives and the gradient in the scalar-valued case
Directional derivatives and partial derivatives of a map
Rectangular matrix multiplication and the identity matrix , including zero-sized shapes
The transpose of a matrix
Linear map between vector spaces over the same field
Invertible matrices and the general linear group
A positive-sized square matrix over a commutative ring is invertible if and only if its determinant is a unit
For , the determinant over a commutative ring by the Leibniz formula, and for a real matrix
Submersions and immersions between Euclidean open sets
Dependency tree · 2 levels
Sources
- D. Tong, Classical Dynamics (Cambridge lecture notes, January 2015 printing), Sections 4.4 and 4.4.3, printed pages 100-105 (PDF pages 106-111): the extension of a configuration-coordinate change to a canonical phase-space map, $P_i=(\Theta^{-1})^{j}{}_{i}\,p_j$, and the generating functions of the various kinds
- G. J. Sussman and J. Wisdom, Structure and Interpretation of Classical Mechanics, second edition (MIT Press, 2014/2015), Sections 5.1 and 5.4.1: point transformations as canonical transformations extending configuration-coordinate changes, and the projection conditions for generating functions