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SUBROUTINE DEM26 (NIN,NOUT)
C$ (DEM26 - Contours of Complex Function)
C$ Demonstration for the representation of a function of a
C$ complex variable. The modulus of the function can be shown
C$ as a surface in three dimensions, but the phase is lost in
C$ the process. By showing contours of constant phase the
C$ lost information is regained, but it is hard to show
C$ contours on a surface already densely populated by linear
C$ arcs. By showing regions of different phase in different
C$ colors the information is presented in a readily
C$ perceivable form.
C$
C$ Alternatively, for typographical reproduction, if colored
C$ printing is unfeasible or too expensive, negative contours
C$ are often drawn with dashed lines to distinguish them from
C$ the solid lines used for positive contours. Various types
C$ of dashing are used for this demonstration. The complex
C$ function plotted has poles at five of the six vertices of a
C$ regular hexagon and is positive. The phase sign is applied
C$ to the modulus, giving a new function in the range
C$ (-infinity,+infinity), which is compressed to the range
C$ (-1,+1) with the hyperbolic tangent function. To avoid
C$ dense contours near the poles, the range plotted is set to
C$ (-0.95,+0.95).
C$
C$ Other views of this function are illustrated in DEM30,
C$ DEM31, DEM32, and DEM34.
C$ (10-APR-82)