© 1997 by London Mathematical Society
© The London Mathematical Society
Planar Harmonic Maps with Inner and Blaschke Dilatations
Department of Mathematics, Johns Hopkins University Baltimore, Maryland 21218-2689, USA. E-mail: laugesen{at}math.jhu.edu
Received 23 February 1995. Revision received 30 June 1995.
A univalent harmonic map of the unit disk
:={z
C:|z|<1} is a complex-valued function f(z) on
that satisfies Laplace's equation
and is injective. The Jacobian
of a univalent harmonic map can never vanish [18], and so we might as well assume that J>0 throughout
. Then |fz|>0 and a short computation verifies that the analytic dilatation
is indeed an analytic function, with |
|<1 since J>0. Clearly 
0 when f is a conformal map, and in general the dilatation
measures how far f is from being conformal. Also, if
happens to be the square of an analytic function, then f lifts to give an isothermal coordinate map for a minimal surface, and in that case i/
equals the stereographic projection of the Gauss map of the surface.
Department of Mathematics, University of Illinois, Urbana Illinois 61801, USA