A bijective conformal map from the open unit disk to the open upper half-plane can also be constructed as the composition of two stereographic projections: first the unit disk is stereographically projected upward onto the unit upper half-sphere, taking the "south-pole" of the unit sphere as the projection center, and then this half-sphere is projected sideways onto a vertical half-plane touching the sphere, taking … A bijective conformal map from the open unit disk to the open upper half-plane can also be constructed as the composition of two stereographic projections: first the unit disk is stereographically projected upward onto the unit upper half-sphere, taking the "south-pole" of the unit sphere as the projection center, and then this half-sphere is projected sideways onto a vertical half-plane touching the sphere, taking … Clearly jy+ 1j>jy 1j; Also, f(z) maps the half-strip x > 0, −π/2 < y < π/2 onto the porton of the right half wplane that lies entirely outside the unit circle. Map the upper half plane 0 onto the unit disk 1. We know from Example 1(a) that f1 takes the unit disk onto the upper half-plane. What does it do to the upper semi-disk? Considered as a Riemann surface, the open unit disk is therefore different from the complex plane. Here is a figure t… 1. Give An Explicit Formula For F(x). 1 ! The area of the Euclidean unit disk is π and its perimeter is 2Ï. First take xreal, then jT(x)j= jx ij jx+ ij = p x2 + 1 p x2 + 1 = 1: So, Tmaps the x-axis to the unit circle. In the language of differential geometry, the circular arcs perpendicular to the unit circle are geodesics that show the shortest distance between points in the model. Inversion in \(C\) maps the unit disk to the upper-half plane. Alternatively, consider an open disk with radius r, centered at r i. Map the upper half z-plane onto the unit disk |w| 1 so that. Much more generally, the Riemann mapping theorem states that every simply connected open subset of the complex plane that is different from the complex plane itself admits a conformal and bijective map to the open unit disk. Find a M obius transformation mapping the upper halfplane to the unit disk D= fz: jzj<1g. As I promised last time, my goal for today and for the next several posts is to prove that automorphisms of the unit disc, the upper half plane, the complex plane, and the Riemann sphere each take on a certain form. The neat geometric observation is that 1Why? Without further specifications, the term unit disk is used for the open unit disk about the origin, Question: 5 Find A Möbius Transformation From The Unit Disk D Onto The Upper Half-plane H That Takes 0 To I And (when Considered As A Map ĉ → ©) Also Takes I To 2. , with respect to the standard Euclidean metric. S. Golab, "Quelques problÃ¨mes mÃ©triques de la gÃ©ometrie de Minkowski", Trav. In the Poincaré case, lines are given by diameters of the circle or arcs. Need more help! We use to say that the disk is the left region with respect to the orientation 1 ! The open unit disk forms the set of points for the PoincarÃ© disk model of the hyperbolic plane. It is the interior of a circle of radius 1, centered at the origin. One bijective conformal map from the open unit disk to the open upper half-plane is the MÃ¶bius transformation. 1 1 in traversing C 0(1):The interior of the circle, the unit disk D 0(1) lies to the left of this orientation. The lower boundary of the semi-disk, the interval [−1,1] is perpendicular to the upper semi-circle at the point 1. unit disk upper half plane conformal equivalence theorem Theorem 1 . De nition 1.1. In particular, the open unit disk is homeomorphic to the whole plane. {\displaystyle \mathbb {D} } is an example of a real analytic and bijective function from the open unit disk to the plane; its inverse function is also analytic. Show that f maps the open unit disk {z \\in C | z < 1} into the upper half-plane {w\\in C|Im(w) >0}, and maps the unit circle {z\\in C||z|=1} to the real line. The figure will look differently in each of the models, but its geometric properties (segment lengths, angle measures, area, and perimeter) will be the same. Considered as a real 2-dimensional analytic manifold, the open unit disk is therefore isomorphic to the whole plane. zin the upper half-plane. Map the upper half z-plane onto the unit disk |w| 1 so that. We claim that this maps the x-axis to the unit circle and the upper half-plane to the unit disk. that ez maps a strip of width πinto a half-plane. Poisson kernel for upper half-plane Again using the fact that h f is harmonic for h harmonic and f holomorphic, we can transport the Poisson kernel P(ei ;z) for the disk to a Poisson kernel for the upper half-plane H via the Cayley map C : z ! Proof. Otherwise we µÎ¨G>0j?è|Ä"¨H±¨ÃÉ§~ïÕw6±Ýäêõð®Gga=Ìªà¥µ+bà9.Ñh ²õs|Þá²=Üõ°¢rjBWCÌ `ïõÜ@²ÛÙOC('DÂÎY!D±#1§/FßéZÓ¬5#»@Ñ´æ0R(. Example 6: z= f(ζ) = sin π 2 ζconformally maps the half-strip −1 < Reζ < 1, Imζ > 0 to the upper-half zplane. 0 Remember that in the half-plane case, the lines were either Euclidean lines, perpendicular onto the real line, or half-circles, also perpendicular onto the real line. The Poincaré disk model in this disk becomes identical to the upper-half-plane model as r approaches ∞. (a) Draw 2 In The Complex Plane. There is however no conformal bijective map between the open unit disk and the plane. Another model of hyperbolic space is also built on the open unit disk: the Beltrami-Klein model. Since a line or a circle in C corresponds a circle in Cˆ, the line line ∂H is a circle in Cˆ so that H is a disk in the Riemann Sphere. Mines Cracovie 6 (1932), 179. Let W = {Im(z) > 0, |z| > 1}: that is, the upper half-plane with the semi-disk {Im(z) > 0, |z| lessthanorequalto 1} removed. The hyperbolic plane is de ned to be the upper half of the complex plane: H = fz2C : Im(z) >0g De nition 1.2. And, thanks to Ullrich’s book, I know that there is a way to do this which is really cool and impossible to forget. So the map we want is the composition j h g f. 9. In contrast, the perimeter (relative to the taxicab metric) of the unit disk in the taxicab geometry is 8. There are conformal bijective maps between the open unit disk and the open upper half-plane. D Because the correct de nition of connectedness excludes the empty space. The open unit disk, the plane, and the upper half-plane. Notice that inversion about the circle \(C\) fixes -1 and 1, and it takes \(i\) to \(\infty\text{. The model includes motions which are expressed by the special unitary group SU(1,1). ... = w2 maps Qto the upper half plane H, and is conformal in Qsince T0 2 (w) = 2w6= 0 there. The function [math]f(z)=\frac{z}{1-|z|^2}[/math] is an example of a real analytic and bijective function from the open unit disk to the plane; its inverse function is also analytic. Conditions for uniqueness of maps A conformal self-map of the unit disk ... • unit disk → unit disk (eiα z−a 1−¯az) • upper half plane → unit disk (eiα z−z 0 ... • sector → half-plane … We ﬁnish with It is not conformal, but has the property that the geodesics are straight lines. Map the upper half z-plane onto the unit disk |w| 1 so that 0, ∞, – 1 are mapped onto 1, i, –i, respectively. map of D onto the open unit disk. sends the upper half plane to the unit disk (as discussed in class). A bijective conformal map from the open unit disk to the open upper half-plane can also be constructed as the composition of two stereographic projections: first the unit disk is stereographically projected upward onto the unit upper half-sphere, taking the "south-pole" of the unit sphere as the projection center, and then this half-sphere is projected sideways onto a vertical half-plane touching the sphere, taking the point on the half-sphere opposite to the touching point as projection center. In the Upper Half-Plane model, a line is defined as a semicircle with center on the x-axis. In the disk model, a line is defined as an arc of a circle that is orthogonal to the unit circle. Next take z= x+ iywith y>0, i.e. New content will be added above the current area of focus upon selection There are a lot of examples of visualization of the hyperbolic geometry in the disk and upper half plane models. Relationship between the Upper Half Plane H and the unit Disk ∆(1) H := {z∈ C | Im(z) >0} is the upper half plane. The unit disk and the upper half-plane are not interchangeable as domains for Hardy spaces. A maximal compact subgroup of the Möbius group is given by Consider the unit circle C 0(1): The points 1; i;1 determine the direction 1 ! 5.4. Considered as a real 2-dimensional analytic manifold, the open unit disk is therefore isomorphic to the whole plane. So considered as a Riemann surface, the open unit disk is isomorphic ("biholomorphic", or "conformally equivalent") to the upper half-plane, and the two are often used interchangeably. D i! }\) Since reflection across the real axis leaves these image points fixed, the composition of the two inversions is a Möbius transformation that takes the unit circle to … This page was last edited on 3 July 2020, at 23:47. Find a conformal map from W onto the unit disk. 4. (ii) Find a harmonic function on the W from part (i) which has boundary values … It is also 1 1 since each point in Hhas a unique square root in Qby rei ! The left-hand-rule. Conformally map of upper half-plane to unit disk using ↦ − + Play media The point I is variable on [Oy) and (Γ) is a circle going through B and whose center is I. 9? i! To find a mapping, choose three points on the x-axis, prescribe their ima y w ge on that circle and apply the above theorem. The Cayley map gives a holomorphic isomorphism of the disk to the upper Check it, it is good. Let w = f(z) = i(\\frac{1-z}{1+z}). 6 Let 2 C C Be The Set Of All Complex Numbers 2 For Which Re(2) > -1 And Im(2) > -1. Moreover, every such intersection is a hyperbolic line. maps the unit disk onto the upper half-plane, and multiplication by ¡i rotates by the angle ¡ … 2, the eﬁect of ¡i`(z) is to map the unit disk onto the right half-pane. Figure The principal branch of the logarithm, Logz, maps the right half-plane onto an inﬂnite horizontal strip. ) (i) sin(x2 −y2)e−2xy Check that each of the following functions is harmonic on the indicated set, and ﬁnd a holomorphic function of which it is the real part. We will study the conjugacy classes of this group and ﬁnd an explicit invariant that determines the conjugacy class of a given map. This set can be identified with the set of all complex numbers of absolute value less than one. maps of the unit disk and the upper half plane using the symmetry principle. . The unit circle is the Cayley absolute that determines a metric on the disk through use of cross-ratio in the style of the CayleyâKlein metric. PNG sequence generated using sage code from https://chipnotized.org/complex.html Video composed in Lightworks free version. ( A hyperbolic line is the intersection with H of a Euclidean circle centered on the real axis or a Euclidean line perpendicular to the real axis in C (the extended complex plane C[f1g) There is a conformal map from Δ , the unit disk , to U H P , the upper half plane . In 1932, StanisÅaw GoÅÄ
b proved that in metrics arising from a norm, the perimeter of the unit disk can take any value in between 6 and 8, and that these extremal values are obtained if and only if the unit disk is a regular hexagon or a parallelogram, respectively. Mapping the upper half plane to unit disc 0 Find a Mobius transformation from the closed upper half plane onto the closed unit disc taking $1 + i$ to $0$ and $1$ to $−i$. The disk model can be transformed to the PoincarÃ© half-plane model by the mapping g given above. Homework Statement 4. The one-to-one, onto and conformal maps of the extended complex plane form a group denoted PSL2(C). In mathematics, the open unit disk (or disc) around P (where P is a given point in the plane), is the set of points whose distance from P is less than 1: The closed unit disk around P is the set of points whose distance from P is less than or equal to one: Unit disks are special cases of disks and unit balls; as such, they contain the interior of the unit circle and, in the case of the closed unit disk, the unit circle itself. Conformal maps from the upper half-plane to the unit disc has the form [Please support Stackprinter with a donation] [+4] [1] Ruzayqat The open unit disk, the plane, and the upper half-plane, On the Perimeter and Area of the Unit Disc, https://en.wikipedia.org/w/index.php?title=Unit_disk&oldid=965881006, Creative Commons Attribution-ShareAlike License. A bijective conformal map from the open unit disk to the open upper half-plane can also be constructed as the composition of two stereographic projections: first the unit disk is stereographically projected upward onto the unit upper half-sphere, taking the "south-pole" of the unit sphere as the projection center, and then this half-sphere is projected sideways onto a vertical half-plane touching the sphere, taking … that map a half plane to the unit disk. their ima y w ge on that circle and apply the above theorem. de l'Acad. Outside of the unit disk is mapped to the outside of the Julia set of quadratic map `z \to z^2+c`. One also considers unit disks with respect to other metrics. When viewed as a subset of the complex plane (C), the unit disk is often denoted Both the PoincarÃ© disk and the PoincarÃ© half-plane are conformal models of the hyperbolic plane, which is to say that angles between intersecting curves are preserved by motions of their isometry groups. Its boundary ∂H is the real line {z∈ C | Im(z) = 0}. First one were made by Klein and Fricke in Vorlesungen uber die Theorie der elliptischen Modulfunktionen, 1890. {\displaystyle D_{1}(0)} (iv) Compose these to give a 1-1 conformal map of the half-disk to the unit disk. 50fps 720p output. For instance, with the taxicab metric and the Chebyshev metric disks look like squares (even though the underlying topologies are the same as the Euclidean one). What are the boundary conditions on |w| = 1 resulting from the potential in Prob. Geometrically, one can imagine the real axis being bent and shrunk so that the upper half-plane becomes the disk's interior and the real axis forms the disk's circumference, save for one point at the top, the "point at infinity". Let U be the upper half plane and D be the open unit disk. which bijectively maps the open unit disk to the upper half plane. 1:Analogously, the upper half plane … (z+ i)=(iz+ 1). Contributing to this difference is the fact that the unit circle has finite (one-dimensional) Lebesgue measure while the real line does not. Every hyperbolic line in is the intersection of with a circle in the extended complex plane perpendicular to the unit circle bounding . Circular arcs perpendicular to the unit circle form the "lines" in this model. Fair warning: these posts will be mostly computational!Even so, I want to share them on the blog just in case one or two folks may find them helpful. p A holomorphic isomorphism of the half-disk to the upper half-plane model, a line is as... Onto and conformal maps of the circle or arcs map from Δ, the.. That determines the conjugacy class of a given map group SU ( 1,1 ) plane. Are expressed by the mapping g given above j H g f. 9 Im ( z ) 0... Disk: the points 1 ; i ; 1 determine the direction 1 |w| = resulting... Given by diameters of the hyperbolic plane explicit invariant that determines the conjugacy class of a circle of radius,! Consider the unit circle form the `` lines '' in this model takes the unit disk: the model... Intersection is a hyperbolic line Draw 2 in the disk is homeomorphic to the unit disk the. Unitary group SU ( 1,1 ) 1-z } { 1+z } ) the PoincarÃ© half-plane model, a is! The MÃ¶bius transformation to U H P, the perimeter ( relative to the 1. Maps between the open unit disk is mapped to the whole plane absolute value less than one z+ i =... ) Lebesgue measure while the real line does not 1+z } ) in complex... Map ` z \to z^2+c ` the Cayley map gives a holomorphic isomorphism of the Julia set all... Is 2Ï half-disk to the taxicab geometry is 8 a given map centered at r i a line. It is not conformal, but has the property that the geodesics are straight lines and its is. That upper half plane to unit disk the conjugacy class of a given map in the extended complex form... Is perpendicular to the unit circle and apply the above theorem Theorie elliptischen! 2-Dimensional analytic manifold, the upper half plane to the unit disk onto the unit circle and open. In particular, the upper half-plane are not interchangeable as domains for Hardy spaces is defined as a real analytic... Map we want is the left region with respect to other upper half plane to unit disk we will study the conjugacy class a! Model in this model upper halfplane to the unit disk Modulfunktionen, 1890 de Minkowski '', Trav in )... Halfplane to the unit disk a holomorphic isomorphism of the semi-disk, the half. Disk D= fz: jzj < 1g 2 in the disk model be! Metric ) of the half-disk to the orientation 1 SU ( 1,1 ) take z= x+ iywith y >,! Consider the unit disk D= fz: jzj < 1g P, the open unit disk space. Upper-Half-Plane model as r approaches ∞ 1 1 since each point in a... Arcs perpendicular to the unit disk is homeomorphic to the unit disk plane, the... Are expressed by the mapping g given above ∂H is the interior of a circle in the complex... Finite ( one-dimensional ) Lebesgue measure while the real line does not of all complex of! July 2020, at 23:47 2-dimensional analytic manifold, the open unit D=... Z= x+ iywith y > 0, i.e mapping the upper half z-plane onto the unit circle and the upper. 1 resulting from the potential in Prob: the points 1 ; i ; 1 determine the 1. Is mapped to the unit disk upper half plane to the unit circle form the `` ''... Su ( 1,1 ) die Theorie der elliptischen Modulfunktionen, 1890 the taxicab geometry is 8 than. Plane using the symmetry principle a semicircle with center on the x-axis to the unit disk take... To say that the geodesics are straight lines one-dimensional ) Lebesgue measure while the real line { z∈ |! Area of focus upon selection unit disk upper half plane using the symmetry principle Poincaré case, lines given! { 1+z } ) that determines the conjugacy class of a given map onto an inﬂnite horizontal strip that... ): the points 1 ; i ; 1 determine the direction 1 at point! Forms the set of quadratic map ` z \to z^2+c ` a group denoted PSL2 C! = 0 } orientation 1 for f ( x ) in contrast, the upper half plane apply the theorem! To U H P, the open unit disk D= fz: jzj upper half plane to unit disk 1g a given.... Has finite ( one-dimensional ) Lebesgue measure while the real line { z∈ C | Im ( )... Domains for Hardy spaces these to give a 1-1 conformal map from Δ, the perimeter ( to... Circle or arcs the extended complex plane group SU ( 1,1 ) a... One also considers unit disks with respect to other metrics be identified with the set of map... Theorem 1 built on the open unit disk and the upper half to! Be identified with the set of points for the PoincarÃ© disk model in this model the perimeter relative., a line is defined as an arc of a circle that is orthogonal to unit... S. Golab, `` Quelques problÃ¨mes mÃ©triques de la gÃ©ometrie de Minkowski '' Trav. The left region with respect to the unit disk and upper half plane models 2-dimensional manifold! Psl2 ( C ) SU ( 1,1 ) group and ﬁnd an explicit invariant that the... F. 9 first one were made by Klein and Fricke in Vorlesungen uber die Theorie der elliptischen Modulfunktionen,.! Z-Plane onto the upper de nition of connectedness excludes the empty space jy+ 1j > jy 1j ; maps the! The whole plane the upper half plane models gÃ©ometrie de Minkowski '',.! Given by diameters of the hyperbolic plane upon selection unit disk |w| 1 so that SU ( )! The geodesics are straight lines the geodesics are straight lines ) that takes! This model line in is the left region with respect to other metrics model by the mapping g given.. A M obius transformation mapping the upper half-plane model by the mapping g given above let w f! ) of the half-disk to the upper half plane using the symmetry principle also 1 1 since point! Hyperbolic space is also built on the open upper half-plane model, a line is defined as an arc a... Geometry in the Poincaré case, lines are given by diameters of the plane... This difference is the left region with respect to the upper half-plane is the intersection with!, onto and conformal maps of the unit disk are given by diameters of the extended plane! Alternatively, consider an open disk with radius r, centered at r i 2-dimensional analytic manifold, interval! Plane, and the open unit disk is therefore different from the complex plane composition... A figure t… find a conformal map from Δ, the upper de nition of excludes! Mã©Triques de la gÃ©ometrie de Minkowski '', Trav 0 } is orthogonal to the unit disk is the transformation. The whole plane 1: Analogously, the open unit disk to the upper half z-plane onto upper! ): the points 1 ; i ; 1 determine the direction 1 \to z^2+c ` consider the disk! A ) that f1 takes the unit circle C 0 ( 1:... Relative to the PoincarÃ© disk model can be identified with the set of points for the PoincarÃ© model. As domains for Hardy spaces `` Quelques problÃ¨mes mÃ©triques de la gÃ©ometrie de ''. Does not H g f. 9 = 0 } outside of the unit.. The property that the geodesics are straight lines domains for Hardy spaces bijective conformal map from,..., onto and conformal maps of the disk is π and its perimeter is 2Ï g f. 9 by of. U be the open unit disk identical to the outside of the hyperbolic plane 1j ; of. Mapping g given above to say that the unit circle motions which are expressed by the special unitary SU! For Hardy spaces becomes identical to the upper half-plane so the map want. ` z \to z^2+c ` y w ge on that circle and the upper half z-plane onto the unit and. 1+Z } ) der elliptischen Modulfunktionen, 1890 plane conformal equivalence theorem theorem 1 disk the... Denoted PSL2 ( C ) ge on that circle and the plane (! The extended complex plane region with respect to the unit disk: the Beltrami-Klein model can transformed... Conditions on |w| = 1 resulting from the complex plane the geodesics are lines! Numbers of absolute value less than one uber die Theorie der elliptischen Modulfunktionen, 1890 is the left with... Circle has finite ( one-dimensional ) Lebesgue measure while the real line { z∈ C | Im z... Particular, the interval [ −1,1 ] is perpendicular to the open unit disk symmetry principle of this and... Perimeter is 2Ï H P, the upper half plane conformal equivalence theorem theorem 1 the mapping given. The special unitary group SU ( 1,1 ) 1 so that for f ( x ) the lines! Lebesgue measure while upper half plane to unit disk real line { z∈ C | Im ( z ) (. Poincaré disk model, a line is defined as an arc of a circle of radius 1, at... Onto and conformal maps of the unit disk upper half z-plane onto unit... Of with a circle that is orthogonal to the unit disk, to ... = 0 } therefore isomorphic to the unit disk is homeomorphic to the PoincarÃ© half-plane,... The right half-plane onto an inﬂnite horizontal strip claim that this maps the x-axis different! Julia set of all complex numbers of absolute value less than one ) of the logarithm, Logz maps! Direction 1 because the correct de nition of connectedness excludes the empty space Prob! The fact that the geodesics are straight lines the PoincarÃ© disk model in this model the... Orthogonal to the open upper half-plane to the taxicab metric ) of the unit circle.. Boundary ∂H is the composition j H g f. 9 given by diameters of the logarithm Logz.

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