(Here "sqrt" means to take the square root.)X = Y - (X/|X|)*sqrt(|aX|)
Y = b - X
The first series of iterations here starts with the initial values X = .9 and Y = 0. The two equations are then iterated 10,000 times, plotting each (X,Y) point of the iteration. Then the starting value for Y is increased slightly, and another 10,000 plots are plotted (see the Java source code for details).
By varying the parameter a in the first equation above (aX is set at 1.53 X for the applet supplied here), and also the rate at which the starting value for Y is increased (set Y = .025*col, say, instead of Y = .047*col), different structures can be obtained.