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FINITE RIEMANN'S MINIMAL SURFACE
Surface studied by David Hoffman and Hermann Karcher
in 1993.
Links: www.indiana.edu/~minimal/archive/Spheres/Planar/FiniteRiemann/web/index.html www.indiana.edu/~minimal/archive/Harmonic/harmonic/(1,2,2)x2+(0,2,2)/web/index.html http://virtualmathmuseum.org/Surface/lopezros/lopezros.html www.indiana.edu/~minimal/research/claynotes.pdf p 29 
Cartesian parametrization:
with .
the views on this page are made with k = 3/10. 
The Riemann finite minimal surface is the minimal
surface obtained by taking
(and then )
in the Weierstrass parametrization of a minimal
surface: .
It has two infinite sheets of the type of those of the
catenoid and an infinite sheet
with an asymptote plane (hence the name "finite", as opposed to Riemann's
original minimal surface that has an infinite number of plane sheets).
Note that if extended, the sheets intersect, contrary
to those of Costa's surface. See here
a surface of the same type, non minimal but harmonic, the sheets of which
do not intersect.
The Riemann finite minimal surface has the same shape as the cubic surfaces with equations and .... 
asymptote cylinder x²+y²=a² 

... or as the sextic surface with equation ,
as well as the transcendental surface with equation .
For both of them, the asymptote lines are the straight lines . 


A Riemann finite surface, by Alain Esculier. 
A Riemann finite surface in wire, by Christoph Soland, Bugnon gymnasium, Lausanne, see at Dyck's surface. 
Engraving of this surface, by Patrice Jeener
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© Robert FERRÉOL 2017