renormalization and chaos in the logistic map. logistic map many features of non-hamiltonian chaos...
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Renormalization and chaos in the logistic map
Logistic map
Many features of non-Hamiltonian chaos can be seen in this simple map(and other similar one dimensional maps).
Why? Universality.
Period doublingIntermittencyCrisisErgodicityStrange attractorsPeriodic/Aperiodic mixTopological Cantor set
Time series
Superstable points; convergence to attractor very rapidCritical slowing down near a bifurcation; convergence very slow
Time series
Superstable points; convergence to attractor very rapidCritical slowing down near a bifurcation; convergence very slow
Time series
Bifurcation to a two cycle attractor
Time series
A series of period doublings of the attractor occur for increasing valuesof r, the “biotic potential” as it is sometimes known for the logistic map
Time series
At a critical value of r the dynamics become aperiodic. However, note thatinitially close trajectories remain close. Dynamics are not ergodic.
Time series
At r = 4 one finds aperiodic motion, in which initially close trajectoriesexponentially diverge.
Self similarity, intermittency, “crisis”
Other one dimensional maps
Other one dimensional maps show a rather similar structure; LHSis the sine map and RHS one that I made up randomly.
In fact the structure of the periodic cycles with r is universal.
Experiment
Universality
2nd order phase transitions: details, i.e. interaction form, does not matternear the phase transition.
Depend only on (e.g.) symmetry of order parameter, dimensionality,range of interaction
Can be calculate from simple models that share these feature with(complicated) reality.
The period doubling regime
• Derivative identical for all points in cycle.• All points become unstable simultaneously; period doubling topology canonly be that shown above.
The period doubling regime
Superstable cycles so called due to accelerated form of convergence;in Taylor expansion first order term vanishes.
Use continuity
The period doubling regime
These constants have been measured in many experiments!
Renormalisation
Change coordinates such that superstablepoint is at origin
Renormalisation
Renormalisation
Renormalisation
Universal mapping functions
Each of these functions is an i cycle attractor.
Doubling operator for g’s
Doubling operator in function space g
Eigenvalues of the doubling operator
Linearize previousequation
Eigenvalues of the doubling operator
This was an assumption of Feigenbaum’s;proved later (1982)
Eigenvalues of the doubling operator
Liapunov exponents
Liapunov exponents
Fully developed chaos at r = 4
Bit shift map
Any number periodic in base 2 leadsto periodic dynamics of the logistic map
Irrational numbers lead to non-periodicdynamics.
Change variables, leads to exact solutionfor this case. (Other cases: r=-2, r=+2).
Ergodicity at r = 4
Strange attractor:
• Fractal• Nearby points diverge under map flow• All points visited: ergodic i.e., topologically mixing
Strange attractor of logistic map (and similarone dimensional maps) is a “topological Cantor set”Lorenz attractor
Ergodic: all points visited
Invarient density