Lyapunov exponent -- Numerical calculations

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Discussion Overview

The discussion centers around the numerical calculations of the largest Lyapunov exponent (LE) in computational physics, particularly its implications for chaos and periodicity in dynamical systems. Participants explore the significance of specific values of LE and the relationship between LE and the nature of motion in phase space.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • Some participants suggest that a positive largest Lyapunov exponent indicates chaos, while a negative or zero exponent suggests a lack of chaos.
  • One participant notes that a more negative LE implies a quicker return to an unperturbed path in phase space.
  • Questions arise about whether a negative LE necessarily means motion is periodic, with some participants proposing that zero LE corresponds to quasiperiodic motion.
  • Another participant highlights the complexity of the situation, mentioning variables such as whether the system is conservative, winding numbers, and dimensions, indicating that a negative LE does not imply periodic orbits.
  • There is a discussion about the relationship between periodic orbits and LE, with one participant asserting that periodic orbits imply a negative LE, while another counters that unstable periodic orbits can have a positive LE.

Areas of Agreement / Disagreement

Participants express differing views on the implications of negative and positive Lyapunov exponents, particularly regarding periodicity and the nature of motion. The discussion remains unresolved with multiple competing perspectives on these relationships.

Contextual Notes

Participants acknowledge the complexity of the topic, noting the influence of various factors such as system conservativeness and the dimensionality of phase space, which may affect the interpretation of Lyapunov exponents.

LagrangeEuler
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In computational physics is very often to calculate largest Lyapunov exponent. If largest Lyapunov exponent ##LE## is positive there is chaos in the system, if it is negative or zero there is no chaos in the system. But what can we say about some certain value of ##LE##. For example ##LE_1=-0.2## and ##LE_2=-0.4##. What is the difference between those particular values? Could we say something in small scales? Thanks for the answer.
 
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The more negative the LE is, the more quickly the trajectory returns to its unperturbed path in that dimension of phase space.
 
Thank you for the answer. Is it necessary that if LE is negative motion is periodic? And when LE is zero motion is quasiperiodic?
 
Too many variables in play for a simple answer. Conservative or not? Winding numbers? Dimensions?

A negative LE does not imply a periodic orbit.
 
Ok thanks. But periodic orbits imply that LE is negative. Right?
 
LagrangeEuler said:
Ok thanks. But periodic orbits imply that LE is negative. Right?

Not always. There are cases of unstable periodic orbits where the LE is positive.

Try a google search for unstable periodic orbits. There are a lot of examples.
 

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