Extreme points and support points of conformal mappings

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There are three types of results in this paper. The first, extending a representation theorem on a conformal mapping that omits two values of equal modulus. This was due to Brickman and Wilken. They constructed a representation as a convex combination with two terms. Our representation constructs convex combinations with unlimited number of terms. In the limit one can think of it as an integration over a probability space with the uniform distribution. The second result determines the sign of RL(z 0 (f(z)) 2 ) up to a remainder term which is expressed using a certain integral that involves the Löwner chain induced by f(z), for a support point f(z) which maximizes RL. Here L is a continuous linear functional on H(U), the topological vector space of the holomorphic functions in the unit disk U = {z ∈ ℂ| |z| < 1}. Such a support point is known to be a slit mapping and f(z 0 ) is the tip of the slit ℂ -f(U). The third demonstrates some properties of support points of the subspace S n of S. S n contains all the polynomials in S of degree n or less. For instance such a support point p(z) has a zero of its derivative p′(z) on ∂ U.

Original languageEnglish
Pages (from-to)23-31
Number of pages9
JournalOpen Mathematics
Issue number1
StatePublished - 17 Feb 2019


  • Conformal mappings
  • Extreme points
  • Schlicht functions
  • Support points

ASJC Scopus subject areas

  • Mathematics (all)


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