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Electronic Geometry Model No. 2002.05.001


Ashay Dharwadker


Riemann surfaces were first studied by Bernhard Riemann in his Inauguraldissertation at Göttingen in 1851.

Consider the function from the complex plane to itself given by w=f(z)=zn, where n is at least 2. The z-plane may be divided into n sectors given by arg z lying between (k-1)(2pi/n) and k(2pi/n) for k=1,...,n. There is a one-to-one correspondence between each sector and the whole w-plane, except for the positive real axis. The image of each sector is obtained by performing a cut along the positive real axis; this cut has an upper and a lower edge. Corresponding to the n sectors in the z-plane, take n identical copies of the w-plane with the cut. These will be the sheets of the Riemann surface and are distinguished by a label k which serves to identify the corresponding sector. For k=1,...,n-1 attach the lower edge of the sheet labeled k with the upper edge of the sheet labeled k+1. To complete the cycle, attach the lower edge of the sheet labeled n to the upper edge of the sheet labeled 1. In a physical sense, this is not possible without self-intersection but the idealized model shall be free of this discrepancy. The result of the construction is a Riemann surface whose points are in one-to-one correspondence with the points of the z-plane. This correspondence is continuous in the following sense. When z moves in its plane the corresponding point w is free to move on the Riemann surface. The point w=0 connects all the sheets and is called the branch point. A curve must wind n times around the branch point before it closes. Now consider the n-valued relation z=nthroot(w). To each nonzero w, there correspond n values of z. If the w-plane is replaced by the Riemann surface just constructed, then each complex nonzero w is represented by n points of the Riemann surface at superposed positions. Let the point on the uppermost sheet represent the principal value and the other n-1 points represent the other values. Then z=nthroot(w) becomes a single-valued, continuous, one-to-one correspondence of the points of the Riemann surface with the points of the z-plane. The Riemann surface is orientable, since every orientation of a sheet is carried over to the sheet next to it.

Model produced with: JavaView v.2.21

KeywordsRiemann Surface; Algebraic Function
MSC-2000 Classification30F99
Zentralblatt No.05264891


  1. B. Riemann: Grundlagen für eine allgemeine Theorie der Functionen einer veränderlichen complexen Grösse, Inauguraldissertation, Göttingen (1851), http://www.emis.de/classics/Riemann/.
  2. D. Hilbert and S. Cohn-Vossen: Anschauliche Geometrie, English Translation by Chelsea Publishing Company (1990) (1932), .


Submission information

Submitted: Sun May 19 09:03:19 CEST 2002.
Revised: Fri Jan 10 14:19:31 GMT 2003.
Accepted: Fri Feb 14 18:02:36 CET 2003.

Author's Address

Ashay Dharwadker
Ansal Institute of Technology
H-501 Palam Vihar
District Gurgaon
Haryana 122017