If you look in the source (http://bl.ocks.org/3914862 http://bl.ocks.org/3914862) about 4/5 of the way down, they basically copy the core logic from Jake's Matp

If you look in the source (http://bl.ocks.org/3914862 http://bl.ocks.org/3914862) about 4/5 of the way down, they basically copy the core logic from Jake's Matplotlib version.