|  Lyapunov Exponents | 
In General > s.a. chaos; entropy;
Mixing System; non-extensive entropy.
  * Idea: A measure of how
    fast nearby orbits in phase space starting from a given point converge or
    diverge from each other; A dynamical system has as many Lyapunov exponents
    as the dimensionality of its phase space.
  * Applications: Widely used
    in celestial mechanics as chaos indicator to characterize the dynamical
    behavior of bodies.
  $ Def: Given two orbits
    initially separated by d(0) in phase space, the corresponding
    Lyapunov exponent is
λ:= limt → ∞ (1/t) ln(d(t)/d(0)) , meaning d(t) ~ d(0) exp{λt} as t → ∞ .
  * Time scale: The time
    tL:= 1/λ over
    which nearby trajectories separate by a factor of e.
  * And attractors: Fixed-point
    attractors yield all negative Lyapunov exponents, periodic orbits a zero one,
    and strange attractors at least one positive one.
  @ References:
    Ginelli et al PRL(07) [covariant Lyapunov vectors];
    Motter & Saa PRL(09)-a0905 [relativistic invariance];
    Slipantschuk et al JPA(13) [and exponential decay of correlations];
    Cencini & Ginelli ed-JPA(13)#25;
    Viana 14,
    Pikovsky & Politi 16 [textbook];
    Wilkinson BAMS-a1608-conf [expository, why they are important].
  > Online resources:
    see MathWorld page;
    Wikipedia page.
Applications and Special Topics > s.a. cellular
  automaton; Kolmogorov-Sinai Entropy.
  @ Calculation:
    Wolf et al PhyD(85) [from time series];
    Habib & Ryne PRL(95)cd/94 [symplectic];
    Kandrup et al PRE(02)ap/01 [and microcanonical distribution];
    Terzić & Kandrup PLA(03)ap/02 [estimate];
    Stachowiak PhD(08)-a0810 [algorithm].
  @ Test bodies in curved spacetime: Wu & Huang PLA(03)gq;
    Wu et al PRD(06)-a1006;
    > s.a. geodesics.
  @ And general relativity dynamics: Motter PRL(03)gq [cosmological models];
    > s.a. chaotic motion;
      chaos in the gravitational field.
  @ Other applications:
    Gerlach a0901-proc [asteroids, numerical].
  @ In quantum mechanics: Man'ko & Vilela Mendes PhyD(00)qp [phase space approach];
    Ballentine PRA(01) [for classical-quantum differences];
    Falsaperla et al FP(02)qp/06;
    Kondratieva & Osborn qp/05-proc [based on Moyal phase space quantization];
    Majewski & Marciniak JPA(06)qp/05;
    Berenstein & García-García a1510 [upper bound on the Lyapunov exponents, and entanglement entropy growth rate].
  @ Finite-time: Aurell et al JPA(97);
    Szezech et al PLA(05) [and dynamical traps of chaotic orbits].
  @ Related topics: Ziehmann et al PLA(00) [local, and predictability];
    Tanase-Nicola & Kurchan JPA(03) [statistical mechanics formulation];
    Baptista et al PLA(11)
      [information production and bound on the sum of positive exponents];
    Akemann et al a1809 [universal local statistics];
    Sutter et al a1905 [analytical upper and lower bounds];
    > s.a. non-extensive statistics [Tsallis entropy].
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