What you get is some very nifty art!
I think most of the patterns in the samples are aliasing ‘artifacts’ of the high frequency components of the functions, in other words, Moiré patterns.
Essentially, any pixel plot of a continuous function is a discrete sampling, and frequency components of 2 x sampling frequency are folded into the < 2 x sampling frequency area.
I remember doing these in the mid 80’s on my first computer in BASIC. Of course, the idea didn’t originate with me; I got it from some computer magazine. I wonder how many times it has been rediscovered since then.
In the image gallery it would be nice to have a link to the expression for that pic.
Finally, I save pictures in pgm, and embedd the formula as a comment in it. Nice (but not space friendly).
Note that my implementation doesn’t quite meet the spec. — it doesn’t iterate over the square (-1,1) but rather (0, size). The differences aren’t substantial in my tests.