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Period-one to radian action-angle rescaling: and preserve
Statement
Let be period-one action-angle coordinates with as supplied by Action-angle coordinates on a saturated proper submersion neighbourhood of a compact connected regular fibre, with the two-form primitive supplied locally and Action and angle coordinates. Use the quotient lift charts and global angle differentials specified in Action-angle coordinates on a saturated proper submersion neighbourhood of a compact connected regular fibre, with the two-form primitive supplied locally. Put , with quotient lift charts from intervals of length less than ; their transitions are translations by , . The induced diffeomorphism is , with inverse . Thus the notation below means , with values in , and its differential is defined by local real lifts. The action domain rescales from to . Define the rescaled coordinates
Then are coordinates on the same chart,
the angles are -periodic (radian-valued), and if a Hamiltonian is with of class in the period-one coordinates then in the radian coordinates it is with and .
Facts & Assumptions
Given: Period-one action-angle coordinates on a chart , with , and the rescaled functions , .
Coordinate calculus ( Euclidean maps and diffeomorphisms, Directional derivatives and partial derivatives of a map ): the rescaling is a linear invertible change of coordinates with constant differential and .
The period-one form (Action and angle coordinates, Action-angle coordinates on a saturated proper submersion neighbourhood of a compact connected regular fibre, with the two-form primitive supplied locally, A phase domain, its canonical one-form and its standard symplectic two-form): on the chart, and this is the standard two-form in the coordinates .
Hamilton's equations in canonical coordinates (The Hamiltonian field of a function on a phase domain is , and the Poisson bracket is ): on a phase domain with coordinates and standard two-form , a function has Hamiltonian field , so its integral curves satisfy and .
Proof
By [F1], for each ; summing over and using [F2] gives . The angle map is well-defined because changing a lift by an integer changes its scaled lift by an element of , and its inverse is the stated quotient map. On each lift chart its differential is the constant scalar . Since this angle diffeomorphism and the action rescaling are bijective and smooth with smooth inverses, are coordinates on the same chart.
The relation becomes ; in the radian chart the two-form is by step 1.1, so [F3] applies there with : and . The chain rule gives , consistent with .
Remarks
- The rescaling is the standard conversion between the period-one convention of Action and angle coordinates and the radian convention used, for instance, in the adiabatic-invariant estimates of the approximation layer; the symplectic form, and with it the canonical structure, is unchanged.
Depends on
Action-angle coordinates on a saturated proper submersion neighbourhood of a compact connected regular fibre, with the two-form primitive supplied locally
Action and angle coordinates
A phase domain, its canonical one-form and its standard symplectic two-form
A map between phase domains preserves the standard two-form iff , and a canonical diffeomorphism carries to
The Hamiltonian field of a function on a phase domain is , and the Poisson bracket is
Euclidean maps and diffeomorphisms
Directional derivatives and partial derivatives of a map
Dependency tree · 2 levels
Sources
- D. Tong, Classical Dynamics (University of Cambridge Part II Mathematical Tripos), Section 4.5.3 (action-angle variables for one-dimensional systems and the 2 pi normalisation), printed pages 108-111
- Ana Cannas da Silva, Lectures on Symplectic Geometry, revised January 2006, Lecture 18 (the Arnold-Liouville theorem; local period and sign conventions are specified here)