Month: April 2021

s_i = 1, -1, 1, -1, …
Center:0.044082+0.464238i , Zoom = 10

Here is a zoom of the top center of Sequence Fractals Part I #2, the little wing above the c=0 shape. This is also home to two-cycle 2.04 in the list in yesterday’s post. 2.05 is a mirror image reflected across the real axis.

s_i = 1, -1, 1, -1, …
Center:-2.21745+0i , Zoom = 800

Same location as yesterday Sequence Fractals Part I #5, with 10x zoom and 50% more color entropy. This is another two-cycle.

A two cycle means . The second iteration comes back to the start point. The second part of the definition excludes fixed points. f is degree 4 polynomial in z and degree 2 in c. With the fixed start point z₀=0 the double iteration in the definition is a degree 8 polynomial in c. It has 8 roots, with 6 left over after removing the fixed points (0 and -3).

Here are the (c-parameter values) of the six two-cycles

2.00:  -3.604653,  0.000000
2.01:  -3.079229,  0.000000
2.02:  -2.217445,  0.000000
2.03:  -0.186836,  0.000000
2.04:   0.044082,  0.464238
2.05:   0.044082, -0.464238

2.00 is Sequence Fractals Part I #4. 2.02 is today’s image. 2.01 is the period 2 bulb (nose) in c = -3, Sequence Fractals Part I #3, and 2.03 is the center of the nose of c = 0, Sequence Fractals Part I #2. 2.04 and 2.05 are the wings above and below the c=0 brot in Sequence Fractals Part I #2.

s_i = 1, -1, 1, -1, …
Center:-2.21745+0i , Zoom = 8

If you look back at Sequence Fractals Part I #1, you will see there is something in the middle, near c=-2, that was cut off from the zooms to the right Sequence Fractals Part I #2 and left Sequence Fractals Part I #3. Here is a zoom of that thing in the middle. I am not sure whether this is a part of the feature as c=-3 or c=0, or if it is something by itself. I am not sure how to define “part of”. I think I will call this a part of c = -3. Notice the satellites are nicely placed at 90 and 45 degrees.

s_i = 1, -1, 1, -1, …
Center:-3.604665+0i , Zoom = 1024

Here is a zoom into the dark spot on the left side of Sequence Fractals Part I #3.

Recall from Sequence Fractals Part I #1 the two-step iteration formula, . Call the center of this image c_this = -3.604665+0i. Then f(f(0,c_this),c_this) = 0. I may (will definitely) get sloppy at times and say that c_this is a 2-cycle. But these are parameter space (c) pictures. z is the variable that is iterated and it is the z orbit has properties like convergence, divergence and being a two cycle. Not the parameter c. I should say that the z₀=0 orbit with the parameter value c = c_this, is a two cycle. Or maybe that c hosts a two-cycle.

But that is too much of a mouthful, so I will from time to time use the technically incorrect expression. And as long as I am being technical, this is a two-cycle of the two-step function. So it is a four-cycle of the original sequence fractal definition.

And as long as I am dwelling in the minutiae… I have been trying to use the same palette for this set of pictures. The previous palette version of this picture was too dark in the area around the mini. I doubled the color entropy (colors change twice as rapidly) to expose more detail.

s_i = 1, -1, 1, -1, …
Center:-3+0i , Zoom = 3.2x.

Here is the other fixed point. Again, a normal looking mset with satellites. The satellites are much smaller. They also seem to appear in a simple pattern, shooting out from each tip or terminal point.

s_i = 1, -1, 1, -1, …
Center:0+0i , Zoom = 1.

, in other words, z₀ is a fixed point for c=0, -3. These are the centers of the two brots in the previous picture.

Here is a closer look at the shape centered at 0. It looks like a well-formed mset. The little disconnected snake-like satellites are about the only clue that this is not a normal Mandelbrot set. In the Mandelbrot set, all of the minis are connected by thin threads. Also notice that the shapes at 0 and -3 (off screen to the left) are not connected.

s_i = 1, -1, 1, -1, …
Center: -1.8+0i, Zoom = 0.4.

The description “combine fractal and sequence” is intentionally vague. Part I will look at the simplest way to combine fractals and sequences, namely “just add”. The sequence in this case is simple, alternating 1 and -1.

Define the follow functions:
.
.
.
f₀ is the first step, of the iteration, f₁ is the second step. The iteration alternates between the two, f₀, f₁, f₀, f₁ … .
f_c(z) = f(z,c) combines the first two steps, and the even orbits are found by iterating f.

For now, we will hide the odd orbit points, and the fact that we have two different functions, and just look into f. f is a degree 4 polynomial, we can leverage some of the experience from z²+c.

The derivative with respect to z is , so z=0 is a critical point (f’=0) for all values of c. was used as the starting point for this all similar these pictures unless otherwise stated. A degree 4 polynomial has three critical points, the other two are the subject of a later post.