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DEM82

       SUBROUTINE  DEM82 (NIN,NOUT)
 C$    (DEM82 - Hilbert Curves)
 C$    This routine demonstrates the translation of the  recursive
 C$    Hilbert curve into a non-recursive stack-based algorithm in
 C$    SFTRAN3.  The code follows  DEM81 (Sierpinski Curves)  very
 C$    closely.
 C$
 C$    Apart from  its  geometrically interesting  shape,  tending
 C$    toward space filling, the principle interest of the Hilbert
 C$    curve here  is that  it  can be  made arbitrarily  long  by
 C$    simply increasing the order, and it therefore may serve  as
 C$    a useful test of plotter speed.
 C$
 C$    A Hilbert curve of order  N has 4**N vertices.  Unlike  the
 C$    Sierpinski curves, the Hilbert curves are not closed.  They
 C$    can be used  as a test  of a polygon  flood fill  algorithm
 C$    which fills up to, but  not including, the boundary  color;
 C$    the flood  fill should  then completely  cover the  display
 C$    surface, except for  the single Hilbert  curve marking  its
 C$    boundary.
 C$
 C$    For amusement,  the curves  are plotted  in five  different
 C$    coordinate systems.
 C$    (19-SEP-85)