Understanding Lyaponov Time & Units

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Discussion Overview

The discussion revolves around the concept of Lyapunov time and its units, particularly focusing on the dimensionality of Lyapunov exponents and their implications in chaotic systems. Participants explore theoretical and practical aspects of these concepts.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes that Lyapunov time is defined as the inverse of the largest Lyapunov exponent and questions the dimensionality of Lyapunov time, suggesting it may be dimensionless.
  • Another participant argues that if the distance between trajectories grows exponentially with time, then the Lyapunov exponent must have dimensions of reciprocal time to maintain dimensional consistency in the exponential function.
  • A different participant mentions that they have only encountered dimensionless Lyapunov exponents in academic papers.
  • One participant suggests that in computer simulations of dynamical systems, it is acceptable to use dimensionless units for position, time, and mass.

Areas of Agreement / Disagreement

Participants express differing views on the dimensionality of Lyapunov exponents and Lyapunov time, indicating that multiple competing perspectives remain without a consensus.

Contextual Notes

There are unresolved questions regarding the assumptions about dimensionality and the definitions used in different contexts, particularly in theoretical versus practical applications.

LagrangeEuler
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In wikipedia text Lyaponov time is defined as inverse of the largest Lyapunov exponent. I have some difficulties with the units. Lyaponov exponents are dimensionless? So Lyaponov time is also then dimensionless? Right? How then in wikipedia article we get Lyaponov time in time units? Could you get me some reasonable explanation?
 

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If the distance between nearby trajectories of a chaotic system grows like ##\exp (\lambda t)##, with ##\lambda## the Lyapunov exponent, then ##\lambda## should have dimensions of reciprocal time, shouldn't it? The argument of an exponential function has to be dimensionless, otherwise the terms of the expansion

##\exp (x) = 1 + x + \frac{1}{2}x^2 + \frac{1}{6}x^3 + \dots##

would have different dimensions.
 
Thanks. But always in papers, I saw just dimensionless Lyapunov exponents.
 
If you're simulating some theoretical dynamical system with a computer program, it doesn't really matter if you set the position coordinates, time and masses to be dimensionless.
 

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