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Consider a commutative 3D algebra $T$ where the nonreal units $x,y$ satisfy

$$x^2 = A_1 + A_3 y $$ $$xy = 1 + B_2 x + B_3 y$$ $$y^2 = C_1 + C_3 y$$

where all the parameters $A_1,A_3,B_2,..$ are real.

Also we want this algebra to be a non-associative algebra.

Squaring a number in this algebra is done by applying the above to arrive at this formula :$[*]$

$$(a + b x + cy)^2 =$$

$$a^2 + b^2 A_1 + 2bc + c^2 C_1 +$$ $$(2ab + 2bc B_2) x + $$ $$(2ac + b^2 A_3 + 2bc B_3 + c^2 C_3 ) y$$

($a,b,c$ are also real)

Now consider the sequence

$z(0) = a + bx + cy = a(0) + b(0) x + c(0) y$

$z(1) = (a+bx+cy)^2 = a(1) + b(1) x + c(1) y$

$z(2) = z(1)^2 = a(2) + b(2) x + c(2) y$

$z(n) = z(n-1)^2 = a(n) + b(n)x + c(n)y$

Where the squares are computed by the formula $*$ above.

Now we wonder about the 3D julia set created by this sequence.

Main question :

So for a given $a,b,c$ and the parameters $A_1,A_3,B_2,...$ when does the sequence converge to infinity ?

Is there some kind of " norm formula " that determines this ?

( compare with complex numbers : if $a^2 + b^2 > 1 $ repeatly squaring converges to infinity, otherwise it does not. )

Secondary question :

When is the Julia set connected ?

Pictures are very much appreciated.

Keep in mind we only consider the non-associative algebra's of this type. Otherwise it is just isomophic to squaring complex numbers anyway.

I assume some julia sets turn out to be fractals.

Will we get pictures like the Mandelbulb ?

https://www.mandelbulb.com/

Closely related :

Is this 3D algebra $T$ power-associative?

Solving a specific polynomial system of equations of degree $2$

mick
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    https://mathr.co.uk/tmp/1-1-1-1-1-1.gif https://mathr.co.uk/tmp/05-05-05-05-05-05.gif here are a couple of pictures of the filled-in Julia set in (a,b,c)-space, the first with all parameters 1, the second with all parameters 0.5 (camera twice as far from the origin). This shows that your norm question is hard to answer. Rendered with FragM's DE-Raytracer with distance estimate calculated with dual numbers for automatic differentiation. Probably I was doing something wrong as there are artifacts even with a tiny "fudge factor" DE multiplier. – Claude Jan 13 '24 at 19:17
  • @Claude Very nice ! Thank you. I love the shape. Seems connected. Looks a bit like the quaterion fractals but more straight curves imo. I wonder, how many fixpoints are there ? Or cycles of length 2 or 3 ? – mick Jan 13 '24 at 23:33

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