Julia sets

Q7a: What is the difference between the Mandelbrot set and a Julia set?
A7a: The Mandelbrot set iterates z^2+c with z starting at 0 and varying c.
The Julia set iterates z^2+c for fixed c and varying starting z values.  That
is, the Mandelbrot set is in parameter space (c-plane) while the Julia set is
in dynamical or variable space (z-plane).

Q7b: What is the connection between the Mandelbrot set and Julia sets?
A7b: Each point c in the Mandelbrot set specifies the geometric structure of
the corresponding Julia set.  If c is in the Mandelbrot set, the Julia set
will be connected.  If c is not in the Mandelbrot set, the Julia set will be a
Cantor dust.

You can see an example Julia set on the WWW at 

Q7c: How is a Julia set actually computed?
A7c: The Julia set can be computed by iteration similar to the Mandelbrot
computation.  Alternatively, points on the boundary of the Julia set can be
computed quickly by using inverse iterations.  This technique is particularly
useful when the Julia set is a Cantor Set.

Q7d: What are some Julia set facts?
A7d: The Julia set of any rational map of degree greater than one is perfect
(hence in particular uncountable and nonempty), completely invariant, equal to
the Julia set of any iterate of the function, and also is the boundary of the
basin of attraction of every attractor for the map.

Julia set references:

1.  A. F. Beardon, _Iteration of Rational Functions : Complex Analytic
Dynamical Systems_, Springer-Verlag, New York, 1991.

2.  P. Blanchard, Complex Analytic Dynamics on the Riemann Sphere, _Bull. of
the Amer. Math. Soc_ 11, 1 (July 1984), pp. 85-141.  This article is a
detailed discussion of the mathematics of iterated complex functions. It
covers most things about Julia sets of rational polynomial functions.
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