Might want to include this animation for understanding the algorithm as listed. However, that algorithm is a bit complicated because it describes the reason for the pattern forming; you could keep it at the end, but I'd suggest describing the result matrix in terms of rectangles: Quadrants 3 and 4 are filled with 1s, as well as quadrant 1.1 and 1.2, then recurse on quadrant 1.4. (where quadrant a.b is the bth quadrant of the ath quadrant, and quadrants are numbered counter-clockwise starting from 1=top right quadrant)

Completed including the one-liner