#z (predefined symbol)

Type	Readable	Writeable	Constant
complex	In fractal formulas and coloring algorithms	In fractal formulas	No

This predefined symbol represents the main variable of the fractal formula. The fractal formula should update the value of z for each iteration. The coloring algorithm can use the value of #z to determine a proper #index value. The predefined symbol #z is also used for periodicity checking.

As an example the code for a Mandelbrot set is shown here. As you can see, the value of #z is updated each iteration, so the coloring algorithm can read it in its loop section.

Mandelbrot {
init:
  z = 0
loop:
  z = z*z + #pixel
bailout:
  |z| < 4
}

Here is a sample coloring algorithm:

Coloring {
init:
  float closest = 1e20
loop:
  float d = |#z|
  ; determine the value of z closest to the origin
  if d < closest 
    closest = d
  endif
final:
  #index = 0.01 * #numiter + 0.1 * closest
}

Note: to avoid unnecessary # prefixes, the # prefix may be omitted before #z in fractal formulas. However, it is required in coloring algorithms.