Fractals/Iterations in the complex plane/jlamination

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Here doubling map is used to analyze dynamics of complex quadratic polynomials. It is dynamical system easier to analyze then complex quadratic map.

Periodic orbits of angles under doubling map

Note that here chord joining 2 points z1 and z2 on unit circle means that $z_2 = z_1^2$. It does not mean that these points are landing points of the same ray.

Some orbits do not cross :

but some do :

Orbit portraits

An orbit portrait can be in two forms:

• list of lists of numbers (common fractions with even denominator)
• image showing rays landing on periodic z points (= partition of dynamic plane)

Note that :

• here chord joining 2 points z1 and z2 on unit circle means that these points are landing points of the same ray. It does not mean that $z_2 = z_1^2$.
• An orbit portrait is a portrait of orbit, which is periodic under complex quadratic map.
• The Julia set has many periodic orbits so it also hase many orbit portraits
• An orbit portrait is combinatorial description of orbit
• (Douady and Hubbard). Every repelling and parabolic periodic point of a quadratic polynomial fc is the landing point of an external ray with rational angle. Conversely, every external ray with rational angle lands either at a periodic or preperiodic point in J(fc ).[1]

Image

Image can be made in three forms :

• image of dynamic plane with Julia set and external rays landing on periodic orbit
• sketch of above image made in :
• standard way : points of orbit are drawn inside unit circle and rays are made by lines joining angle ( point on unit circle) and point of orbit. It looks like sketch of above image
• hyperbolic way : points are on unit circle and here chord joining 2 points z1 and z2 on unit circle means that these points are landing points of the same ray. It does not mean that $z_2 = z_1^2$. Chord is drawn using arc ( part of orthogonal circle ).

Lamination of Julia sets

"Laminations were introduced to the context of polynomial dynamics in the early 1980’s by Thurston"[2] Are used to show the landing pattern of external rays.

The lamination L gives :

• a combinatorial description of the dynamics of quadratic map.[3] because action of doubling map on the unit circle is a model of action of complex polynomial on complex plane[4]
• exact topological structure of Julia sets [5] = topological model for Julia set
• the model of ray portraits. The external rays for angles in a lamination land at "cut points" of the Julia set / Mandelbrot set.

Note that here chord joining 2 points z1 and z2 on unit circle means that these points are landing points of the same ray. It does not mean that $z_2 = z_1^2$.

For a quadratic polynomials initial set has a form :[6]

$\left \{ \theta , \theta +\frac{1}{2} \right \rbrace$

?????

Definition

Laminations of the unit disk in the plane is a closed collection of chords (leaves, arcs ) inside the unit disk

quadratic laminations = those that remain invariant under the angle doubling map [7]

Notation

• chord = leaf = continuous path on the unit disc identifying (connecting) two points on the unit circle
• pullback = a pullback process = backward iteration

Properities of lamination

Lamination must satisfy the following rules :

• leaves do not cross, although thay may share endpoints
• lamination is forward and backward invariant (under doubling map)

Invariance of lamination

"Invariance of a lamination L in the unit disc means that:

• whenever there is a leaf of L joining $z_1$ and $z_2$ , there is also a leaf of L joining $z_1^2$ and $z_2^2$
• whenever there is a chord joining $z_1$ and $z_2$ , there are points $\pm z_3^2$ and $\pm z_4^2$ with $z_3^2 = z_1$ and $z_4^2 = z_2$ , and such that there are leaves of L joining z3 to z4 , and −z3 to −z4 ."[8]

Tools

Tools used to study dynamics of lamiantions :

• Central Strip Lemma [9]

Drawing lamination

• Drawlam : program for rendering laminations by Clinton P. Curry [10]. This program is licensed under a modified BSD-style license. It uses input file or reads from console.
• Invariant lamination calculator Java applet by Danny Calegari. It computes the invariant lamination for a connected Julia set on the boundary of the Mandelbrot set with variable external angle. With Java src code
• lamination by Danny Calegari. Cpp program for X11 using uses standard Xlib stuff. Source code is released under the terms of the GNU GPL. This program is a toy to do experiments with laminations of the circle. Represents it symbolically and pictorially. It needs only one input : the size of the lamination ( the number of endpoints of polygons). This set of endpoints is enumerated from 0 to size-1 in anticlockwise order. For each endpoint, the nextleaf points to the adjacent endpoint in the anticlockwise direction.

I have changed in main.cc :

#include <math.h>
#include <iostream> // I have removed .h
#include <stdlib.h>
#include "graphics.cc"
using namespace std; // added because : main.cc:101: error: ‘cout’ was not declared in this scope


and then in program directory :

make
./lamiantion


Examples

cut points of order 2

period one orbit = fixed point

For complex quadratic polynomials $f_c(z)$ for all parameters c in wake bounded by rays 1/3 and 2/3 there is repelling fixed point with orbit portrait :

${\mathcal P}({\mathcal O}) = \left \{ {\mathcal A}_1 \right \rbrace = \left \{ \left(\frac{1}{3},\frac{2}{3} \right) \right \rbrace$

cut points of order 3

period one orbit = fixed point

Orbit under quadratic map consists of one ( fixed point) :

${\mathcal O} = \left \{ z_1 \right \rbrace = \left \{ \alpha_c \right \rbrace$

This point is a landing point of 3 external rays and has orbit portrait :

${\mathcal P}({\mathcal O}) = \left \{ {\mathcal A}_1 \right \rbrace = \left \{ \left(\frac{1}{7},\frac{2}{7},\frac{4}{7} \right) \right \rbrace$

period 2 orbit

c is a root point of Mandelbrot set between period 2 and 6 components :[11]

$c= -1 + \frac{1}{4} e^{2\pi i \frac{2}{3}} \in \partial M$

with internal address 1-2-6.

Six periodic cycle of rays is landing on two-periodic parabolic orbit :

${\mathcal O} = \left \{ z_{2,1} , z_{2,2} \right \rbrace$

where :

$z_{2,1} = -\frac{1}{2} + \frac{1}{2} \sqrt{1 - e^{2\pi i \frac{2}{3}}}$

$z_{2,2} = -\frac{1}{2} - \frac{1}{2} \sqrt{1 - e^{2\pi i \frac{2}{3}}}$

with orbit portrait :

${\mathcal P}({\mathcal O}) = \left \{ {\mathcal A}_1, {\mathcal A}_2 \right \rbrace = \left \{ \left(\frac{22}{63},\frac{25}{63},\frac{37}{63} \right) , \left(\frac{44}{63},\frac{50}{63},\frac{11}{63} \right) , \right \rbrace$

period 3 orbit

Parameter c is a center of period 9 hyperbolic component of Mandelbrot set

$c= -0.03111+0.79111*i$

Orbit under quadratic map consists of 3 points :

${\mathcal O} = \left \{ z_{3,1} , z_{3,2}, z_{3,1} \right \rbrace$

orbit portrait associated with parabolic period 3 orbit ${\mathcal O}$ is :[12]

${\mathcal P}({\mathcal O}) = \left \{ {\mathcal A}_1, {\mathcal A}_2, {\mathcal A}_3 \right \rbrace= \left \{ \left(\frac{74}{511},\frac{81}{511},\frac{137}{511} \right) , \left(\frac{148}{511},\frac{162}{511},\frac{274}{511} \right) , \left(\frac{296}{511},\frac{324}{511},\frac{37}{511} \right) \right \rbrace$

Valence = 3 rays per orbit point ( = each point is a landing point of 3 external rays )

Rays for above angles land on points of that orbit .

Questions

• How to comput orbit portraits ?
• How orbit portrait changes when I move inside Mandelbrot set ?