Mandelbrot sets
I started experimenting with visualizing fractals. At first I tried to do it on my own, by looking at the (actually not super complicated but still a bit beyond my understand) Wiki article about the Mandelbrot set:
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Then WikiHow of all things came to my aid and I slowly figured it out:
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All of these are about 2x the actual rendering speed, apart from the final one which somehow runs at 4x speed despite telling it otherwise!! Anyway, this was a really fun diversion. Not useful, though, I think.