DescriptionErays.png	English: Polar coordinate system and mapping from the complement (exterior) of the closed unit disk to the complement of the filled Julia set for ${\displaystyle c=-2}$. Polski: Układ współrzędnych biegunowych oraz funkcja odwzorowująca dopełnienie dysku jednostkowego na dopełnienie zbioru Julia.
Date	4 November 2008 (original upload date)
Source	Own work by uploader in Maxima and Gnuplot with help of many people (see references)
Author	Adam majewski
Other versions	File:Erays.svg is a vector version of this file. It should be used in place of this PNG file when not inferior. File:Erays.png → File:Erays.svg For more information, see Help:SVG. In other languages Alemannisch ∙ العربية ∙ беларуская (тарашкевіца) ∙ български ∙ বাংলা ∙ català ∙ нохчийн ∙ čeština ∙ dansk ∙ Deutsch ∙ Ελληνικά ∙ English ∙ British English ∙ Esperanto ∙ español ∙ eesti ∙ euskara ∙ فارسی ∙ suomi ∙ français ∙ Frysk ∙ galego ∙ Alemannisch ∙ עברית ∙ hrvatski ∙ magyar ∙ հայերեն ∙ Bahasa Indonesia ∙ Ido ∙ italiano ∙ 日本語 ∙ ქართული ∙ 한국어 ∙ lietuvių ∙ македонски ∙ മലയാളം ∙ Bahasa Melayu ∙ norsk bokmål ∙ Plattdüütsch ∙ Nederlands ∙ norsk nynorsk ∙ norsk ∙ occitan ∙ polski ∙ prūsiskan ∙ português ∙ português do Brasil ∙ română ∙ русский ∙ sicilianu ∙ Scots ∙ slovenčina ∙ slovenščina ∙ српски / srpski ∙ svenska ∙ தமிழ் ∙ ไทย ∙ Türkçe ∙ татарча / tatarça ∙ українська ∙ vèneto ∙ Tiếng Việt ∙ 中文 ∙ 中文（中国大陆） ∙ 中文（简体） ∙ 中文（繁體） ∙ 中文（马来西亚） ∙ 中文（新加坡） ∙ 中文（臺灣） ∙ 中文（臺灣） ∙ +/−
Source code InfoField	Created using Maxima. R_max: 5; R_min: 1; dR: R_max - R_min; psi(w) := w+1/w; NmbrOfRays: 10; iMax: 100; /* number of points to draw */ GiveCirclePoint(t) := R*%e^(%i*t*2*%pi); /* gives point of unit circle for angle t in turns */ GiveWRayPoint(R) := R*%e^(%i*tRay*2*%pi); /* gives point of external ray for radius R and angle tRay in turns */ /* f_0 plane = W-plane */ /* Unit circle */ R: 1; circle_angles: makelist(i/(10*iMax), i, 0, 10*iMax-1); /* more angles = more points */ CirclePoints: map(GiveCirclePoint, circle_angles); /* External circles */ circle_radii: makelist(R_min+i, i, 1, dR); WCirclesPoints: []; for R in circle_radii do WCirclesPoints: append(WCirclesPoints, map(GiveCirclePoint, circle_angles)); /* External W rays */ ray_radii: makelist(R_min+dR*i/iMax, i, 0, iMax); ray_angles: makelist(i/NmbrOfRays, i, 0, NmbrOfRays-1); WRaysPoints: []; for tRay in ray_angles do WRaysPoints: append(WRaysPoints, map(GiveWRayPoint, ray_radii)); /* f_c plane = Z plane = dynamic plane */ /* external Z rays */ ZRaysPoints: map(psi, WRaysPoints); /* Julia set points */ JuliaPoints: map(psi, CirclePoints); Equipotentials: map(psi, WCirclesPoints); /* Mario Rodríguez Riotorto (http://www.telefonica.net/web2/biomates/maxima/gpdraw/index.html) */ load(draw); draw( file_name = "erays", pic_width = 1000, pic_height = 500, terminal = 'png, columns = 2, gr2d( title = " unit circle with external rays & circles ", point_type = filled_circle, points_joined = true, point_size = 0.34, color = red, points(map(realpart, CirclePoints),map(imagpart, CirclePoints)), points_joined = false, color = black, points(map(realpart, WRaysPoints), map(imagpart, WRaysPoints)), points(map(realpart, WCirclesPoints), map(imagpart, WCirclesPoints)) ), gr2d( title = "Image under psi(w):=w+1/w; ", points_joined = true, point_type = filled_circle, point_size = 0.34, color = blue, points(map(realpart, JuliaPoints),map(imagpart, JuliaPoints)), points_joined = false, color = black, points(map(realpart, ZRaysPoints),map(imagpart, ZRaysPoints)), points(map(realpart, Equipotentials),map(imagpart, Equipotentials)) ) );

Here are two diagrams:

• on the left is dynamical plane for ${\displaystyle c=0\,}$
• on the right is dynamical plane for ${\displaystyle c=-2\,}$

On left diagram one can see:

• Julia set (unit circle) in red
• concentric circles outside unit circle
• external rays (radial lines outside unit circle)

Right diagram is image of left diagram under function ${\displaystyle \Psi _{c}\,}$ (the Riemann map) which maps the complement (exterior) of the closed unit disk ${\displaystyle {\overline {\mathbb {D} }}}$ to the complement of the filled Julia set ${\displaystyle \ Kc}$

${\displaystyle \Psi _{c}:\mathbb {\hat {C}} \setminus {\overline {\mathbb {D} }}\to \mathbb {\hat {C}} \setminus Kc}$

For ${\displaystyle c=-2\,}$:

${\displaystyle \Psi _{-2}(w)=w+{\frac {1}{w}}\,}$

It is:

• a simplest case for analysis,
• only one case when formula for computing ${\displaystyle \Psi _{c}\,}$ is known (explicit Riemann mapping).

${\displaystyle \Psi _{-2}\,}$ maps ^[1]:

• red unit circle ${\displaystyle {w:abs(w)=1}\,}$ to blue line segment ${\displaystyle {z:z\in [-2,2]}\,}$ (Julia sets)
• concentric circles to ellipses (equipotential lines)
• rays of unit circle to hyperbolas (external rays)

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