This section of the page has always been mediocre. I was trying to explore what the different loops produced. But that's focused on the inputs and what the reader really cares about are which loops actually produce the desired outputs.
In addition, the sample code always put 0,0 at the top left but the diagrams put 0,0 in the center.
I've rewritten this section. The sample code now works for top left or center, and the diagrams show what the reader wants, not all the other permutations of loops.