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+############################################################################
+#
+#	File:     julia1.icn
+#
+#	Subject:  Program to display the Julia set
+#
+#	Author:   Ralph E. Griswold
+#
+#	Date:     June 17, 1994
+#
+############################################################################
+#
+#   This file is in the public domain.
+#
+############################################################################
+#
+#  This is a barebones version of a display of the Julia set.  It
+#  has deliberately been left simple and free of options so that the
+#  basic idea is clear and so that it can be used as the basis of
+#  more capable versions.
+#
+#  This program is based on material given in "Chaos, Fractals,
+#  and Dynamics", Robert L. Devaney, Addison-Wesley, 1990.
+#
+#  The point in the complex plane for which the Julia set is computed
+#  is given on the command line, as in
+#
+#	julia1 .360284 .100376
+#
+#  which displays the Julia set for the complex number .360284 + .100376i.
+#
+############################################################################
+#
+#  Requires:  Version 9 graphics
+#
+############################################################################
+#
+#  Links:  wopen
+#
+############################################################################
+
+link wopen
+
+procedure main(argl)
+   local c1, c2, extent, half, quarter, m, n, x0, y0, x, y
+   local x1, y1, i, z
+
+   c1 := real(argl[1]) | -1.0		# default is -1.0 + 0.0i
+   c2 := real(argl[2]) | 0.0
+
+   extent := 200
+   half := 200 / 2
+   quarter := real(extent) / 4
+
+   WOpen("label=julia", "height=" || extent, "width=" || extent) |
+      stop("*** cannot open window")
+
+   every m := 0 to extent do {
+      x0 := -2 + m / quarter
+      every n := 0 to half do {
+         y0 := 2 - n / quarter
+         x := x0
+         y := y0
+         every i := 1 to 20 do {	# compute orbit
+            x1 := x ^ 2 - y ^ 2 + c1
+            y1 := 2 * x * y + c2
+            x := x1
+            y := y1
+            z := x ^ 2 + y ^ 2
+            if z > 4 then break next	# if escaping, forget it
+            }
+         DrawPoint(m, n)
+         DrawPoint(extent - m, extent - n)
+         }
+      }
+
+   Event()
+
+end