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1989-02-20
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The program riemannmap implements W. Thurston's algorithm for
approximating conformal maps by circle packing isomorphisms. B. Rodin
and D. Sullivan have proved convergence of this scheme to the Riemann
mapping for simply-connected domains. Furthermore, X.S. He and Rodin
have recently proved that the ratio of range radii to domain radii
converges to the norm of the derivative of the Riemann map. The program
also supports the mapping of domains of any finite connectivity, and
runs as follows:
Use the mouse to draw any sequence of closed loops on the screen.
Choose a filling radius and fill the region bounded by the
loops with the regular hexagonal packing of chosen mesh.
The program then does an N-dimensional damped Newton method
to construct an isomorphic packing of the disk (minus holes,
if the domain was multiply-connected). Here, N is roughly
the number of circles. The Yale sparse matrix package
smpak (rewritten in C) is invoked to solve the Newton linear system. Full
use is made of the smpak compact matrix storage scheme,
so no memory of order greater than the number of circles
is ever allocated. A color scheme was implemented which
assigns colors constant on hexagons concentric with the
domain circle which gets sent to the origin. Upon convergence
of the algorithm, the user is allowed to choose a different
nullcircle by clicking with the mouse.
Note that the circles' data is stored in a matrix
with the following special pattern:
0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 9 9 9 0 0 0 0
0 0 0 9 2 2 9 0 0 0 0
0 0 9 2 2 2 9 0 0 0 0
0 0 9 2 2 9 0 0 0 0 0
0 0 9 9 9 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
Column indices j increment from left to right.
Row indices i increment from top to bottom.
For more specifics, see the comments in the source code.