Discrete quasiconformal mappings

Summary Some basic properties of quasiconformal mappings are reviewed which leads to the development of discrete analogs of quasiconformal mappings of a multiply connected domain onto a rectangular domain with slits. These discrete mappings can be constructed by solving a system of equations. Comparison of results for a special conformal mapping suggest that the discrete mapping is a good approximation to the quasiconformal mapping.

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Zusammenfassung Es werden einige grundlegende Eigenschaften quasikonformer Abbildungen diskutiert, und es wird ein diskretes Analogon solcher Abbildungen aufgestellt, mit Hilfe dessen mehrfach zusammenhängende Bereiche auf Rechteckbereiche mit Schlitzen abgebildet werden können. Ein Vergleich der Resultate für eine spezielle konforme Abbildung zeigt, dass die diskrete Abbildung eine gute Approximation der quasikonformen Abbildung liefert.

     

Numerical conformal mapping of multiply connected regions onto the second, third and fourth categories of Koebe?s canonical slit domains

This paper presents a boundary integral method for approximating the conformal mappings from any bounded or unbounded multiply connected region G onto the second, third and fourth categories of Koebe?s canonical slit domains. The method can be also used for calculating the conformal mappings of simply and doubly connected regions. The method is an extension of the author?s method for the first category of Koebe?s canonical slit domains (see [M.M.S. Nasser, Numerical conformal mapping via a boundary integral equation with the generalized Neumann kernel, SIAM J. Sci. Comput. 31 (2009) 1695-1715]). Three numerical examples are presented to illustrate the performance of the proposed method.     

Doubly Connected Minimal Surfaces and Extremal Harmonic Mappings

The concept of a conformal deformation has two natural extensions: quasiconformal and harmonic mappings. Both classes do not preserve the conformal type of the domain, however they cannot change it in an arbitrary way. Doubly connected domains are where one first observes nontrivial conformal invariants. Herbert Gr?tzsch and Johannes C.C.?Nitsche addressed this issue for quasiconformal and harmonic mappings, respectively. Combining these concepts we obtain sharp estimates for quasiconformal harmonic mappings between doubly connected domains. We then apply our results to the Cauchy problem for minimal surfaces, also known as the Bj?rling problem. Specifically, we obtain a sharp estimate of the modulus of a doubly connected minimal surface that evolves from its inner boundary with a given initial slope.     

Finite Element Approximation of Conformal Mappings to Unbounded Jordan Domains

In two-dimensional Euclidean space, a simply connected unbounded domain whose boundary is a Jordan curve is called an unbounded Jordan domain. In this article, we discuss a piecewise linear finite element approximation of conformal mappings from the unit disk of the plane to unbounded Jordan domains. Some convergence results and error analysis are presented. Numerical examples are also given.     

Some problems of conformal mappings of spherical domains

In this study the problem of finding the conformal mapping from a sphere onto a plane with a given scale function independent of longitude is solved for an arbitrary spherical domain. The obtained results are compared with the well-known projections used in cartography and geophysical fluid dynamics. The problem of minimization of the distortion under conformal mappings is solved for domains in the form of the spherical disk. The distortions of some extensively used conformal mappings are compared with the distortions of orthogonal mappings.     

Some problems of conformal mappings of spherical domains

In this study the problem of finding the conformal mapping from a sphere onto a plane with a given scale function independent of longitude is solved for an arbitrary spherical domain. The obtained results are compared with the well-known projections used in cartography and geophysical fluid dynamics. The problem of minimization of the distortion under conformal mappings is solved for domains in the form of the spherical disk. The distortions of some extensively used conformal mappings are compared with the distortions of orthogonal mappings.     

Quasiconformal harmonic mappings between \fancyscriptC1,m{{\fancyscript{C}}^{1,\mu}} Euclidean surfaces

The conformal deformations are contained in two classes of mappings quasiconformal and harmonic mappings. In this paper we consider the intersection of these classes. We show that, every K quasiconformal harmonic mapping between surfaces with boundary is a Lipschitz mapping. This extends some recent results of several authors where the same problem has been considered for plane domains. As an application it is given an explicit Lipschitz constant of normalized isothermal coordinates of a disk-type minimal surface in terms of boundary curve only. It seems that this kind of estimates are new for conformal mappings of the unit disk onto a Jordan domain as well.     

A simplified Fornberg-like method for the conformal mapping of multiply connected regions—Comparisons and crowding

We present a new Fornberg-like method for the numerical conformal mapping of multiply connected regions exterior to circles to multiply connected regions exterior to smooth curves. The method is based on new, symmetric conditions for analytic extension of functions given on circular boundaries. We also briefly discuss a similar method due to Wegmann and compare some computations with both methods. Some examples of regions which exhibit crowding of the circles are also presented.     

On the approximate conformal mapping of multiply connected domains

Summary A method is presented for constructing approximations to the standard mappings for multiply connected regions given by Nehari [5]. The case of mapping onto a slit annulus is considered in detail, and computational results are presented for several examples.     

Conjugate function method for numerical conformal mappings

We present a method for numerical computation of conformal mappings from simply or doubly connected domains onto so-called canonical domains, which in our case are rectangles or annuli. The method is based on conjugate harmonic functions and properties of quadrilaterals. Several numerical examples are given.     

Transboundary extremal length

We introduce two basic notions, ‘transboundary extremal length’ and ‘fat sets’, and apply these concepts to the theory of conformal uniformization of multiply connected planar domains. A new short proof is given to Koebe's conjecture in the countable case: every planar domain with countably many boundary components is conformally equivalent to a circle domain. This theorem is further generalized in two direction. We show that the same statement is true for a wide class of domains with uncountably many boundary components, in particular for domains bounded byK-quasicircles and points. Moreover, these domains admit more general uniformizations. For example, every circle domain is conformally equivalent to a domain whose complementary components are heart-shapes and points. Incumbent of the William Z. and Eda Bess Novick Career Development Chair. Supported by NSF grant DMS-9112150.     

On grid generation for numerical models of geophysical fluid dynamics

A simple geometric condition that defines the class of classical (stereographic, conic and cylindrical) conformal mappings from a sphere onto a plane is derived. The problem of optimization of computational grid for spherical domains is solved in an entire class of conformal mappings on spherical (geodesic) disk. The characteristics of computational grids of classical mappings are compared for different spherical radii of geodesic disk. For a rectangular computational domain, the optimization problem is solved in the class of classical mappings and respective area of the spherical domain is evaluated.     

Linear integral equations for conformal mapping of bounded multiply connected regions onto a disk with circular slits

In this paper we present a boundary integral equation method for the numerical conformal mapping of bounded multiply connected region Ω onto a disk with circular slits. The method is based on some uniquely solvable boundary integral equations with classical adjoint and generalized Neumann kernels. These boundary integral equations are constructed from a boundary relationship satisfied by a function analytic on a multiply connected region. Some numerical examples are presented to illustrate the efficiency of the presented method.     

Commutation relations for Schramm‐Loewner evolutions

Schramm‐Loewner evolutions (SLEs) describe a one‐parameter family of growth processes in the plane that have particular conformal invariance properties. For instance, SLE can define simple random curves in a simply connected domain. In this paper we are interested in questions pertaining to the definition of several SLEs in a domain (i.e., several random curves). In particular, we derive infinitesimal commutation conditions, discuss some elementary solutions, study integrability conditions following from commutation, and show how to lift these infinitesimal relations to global relations in simple cases. The situation in multiply connected domains is also discussed. © 2007 Wiley Periodicals, Inc.     

Multiply Connected Quadrature Domains and the Bergman Kernel Function

This paper derives general analytical formulae for the conformal maps from multiply connected circular preimage domains to multiply connected quadrature domains by considering the Bergman kernel functions of the preimage and target domains. The new formulae are expressed in terms of the Schottky–Klein prime function. They generalize, to the case of arbitrary connectivity, a formula relevant to doubly connected domains derived by Y. Avci in 1977. Submitted: September 17, 2007. Accepted: June 5, 2008.     

Approximation quasikonformer Abbildungen mehrfach zusammenhängender Gebiete durch finite Elemente

Zusammenfassung In dieser Arbeit werden quasikonforme Abbildungen mehrfach zusammenhängender Gebiete auf Rechteckgebiete mit Schlitzen behandelt. Real- und Imaginärteil einer solchen Abbildung können mit Hilfe der zugehörigen Beltrami-Differentialgleichung durch Minimalprinzipien charakterisiert werden. In polygonalen Gebieten werden diese Minimalprinzipien durch Ritz-Ansatz mit finiten Elementen diskretisiert und Fehleralschätzungen angegeben.

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Summary In this note quasiconformal mappings of multiply connected domains onto rectangular domains with slits are considered. Real and imaginary parts of such a mapping can be described by minimal-principles by using the corresponding Beltrami differential equation. In a polygonal domain the discretization of these minimal-principles is carried out by the use of the Ritz method and finite elements. Error bounds are given.

     

Robin functions and distortion theorems for regular mappings

Capacities of generalized condensers are applied to prove a two‐point distortion theorem for conformal mappings. The result is expressed in terms of the Robin function and the Robin capacity with respect to the domain of definition of the mapping and subsets of the boundary of this domain. The behavior of Robin function under multivalent functions is studied. Some corollaries and examples of applications to distortion theorems for regular functions are given (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

An analytical formula for the effective conductivity of 2D domains with cracks of high density

We construct the conformal mapping of the square with circular non-overlapping holes onto the square with non-overlapping slits. It is constructed as a solution of the Riemann–Hilbert problem for a multiply connected domain in a class of double periodic functions. The Riemann–Hilbert problem is reduced to a system of functional equations which is solved with an arbitrary order of approximations. On the basis of this conformal mapping, an analytical formula for the effective conductivity of randomly distributed cracks in 2D media is deduced. This formula extends the known before formulae to high density fractures in 2D media.     

The Carathéodory topology for multiply connected domains I

We consider the convergence of pointed multiply connected domains in the Carathéodory topology. Behaviour in the limit is largely determined by the properties of the simple closed hyperbolic geodesics which separate components of the complement. Of particular importance are those whose hyperbolic length is as short as possible which we call meridians of the domain. We prove continuity results on convergence of such geodesics for sequences of pointed hyperbolic domains which converge in the Carathéodory topology to another pointed hyperbolic domain. Using these we describe an equivalent condition to Carathéodory convergence which is formulated in terms of Riemann mappings to standard slit domains.