Nonlinear stability beyond the Hessian
Research context
postgraduate concept · established · As of 2026-10-10
A positive-definite local energy difference can prove Lyapunov stability of an isolated equilibrium even when its quadratic Hessian is degenerate.
Key knowledge
A positive-definite local energy difference can prove Lyapunov stability of an isolated equilibrium even when its quadratic Hessian is degenerate. For the explicit one-dimensional H=p²/(2m)+a q⁴ with m,a>0, H−H(0) is positive away from the origin and conserved: stability follows although the linear restoring frequency is zero. Conservation alone does not imply attraction.
Values and equations
H=p²/(2m)+a q⁴; dH/dt=0
- H
- Mechanical energy J
- p
- Momentum kg m s⁻¹
- m
- Mass kg
- q
- Displacement m
- a
- Positive quartic coefficient J m⁻⁴
Conditions and scope
- Locally Lipschitz dynamics, isolated minimum and sufficiently small compact energy sublevel contained in the domain.
- A semidefinite Lyapunov function or purely imaginary linear eigenvalues are inconclusive without further nonlinear/invariant-set analysis. Dissipative attraction requires additional hypotheses.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Inspected slides 22–3 to 22–8 and 22–12 to 22–13: regularity, positive-definite functions and invariant sets; source check dated 2026-10-10. Scope is limited to the cited statements, equations and assumptions, not the whole publication.
2026-10-10 · Author source inspection of the displayed claim, model assumptions and equations; independent exact-content and branch-inventory review is a separate gate. Contemporary status is a dated snapshot, not a promise of ongoing monitoring.
Entry details
Permanent link to this entry ↗- Record identity
- research-physics-degenerate-stability
- Revision
- research.1
- Structured reference record
- Postgraduate & research reference