-2 belongs to the Mandelbrot set

[rs1729]

Thanks for the nice lectures!

Your escape check in
VGA_Graphics/Mandelbrot_Set/mandelbrot_fixvfloat.c
should be |z|^2 > 4, and not

Hunter-Adams-RP2040-Demos/VGA_Graphics/Mandelbrot_Set/mandelbrot_fixvfloat.c

Line 101 in f5f85ba

if ((Zre_sq + Zim_sq) >= 4.0) break ;

Hunter-Adams-RP2040-Demos/VGA_Graphics/Mandelbrot_Set/mandelbrot_fixvfloat.c

Line 188 in f5f85ba

if ((Zre_sq + Zim_sq) >= FOURfix28) break ;

The parameter c=-2 belongs to the Mandelbrot set. For this parameter the critical point is pre-periodic (0 -> -2 -> 2 -> 2 -> ...), so it is bounded and the corresponding Julia set is connected (it is the interval [-2,2] on the real axis).
If the orbit gets outside of radius 2, you can show that it escapes to infinity, i.e. that the parameter is not in the Mandelbrot set.