Draws iterated functions fractals.
nb is the number of pixels drawn.
Draw a tree: m=350 w.append([[0,0],[0,.5]]); b.append([[0],[0]]); p.append(.05) w.append([[.42,-.42],[.42,.42]]); b.append([[0],[.2]]); p.append(p[-1]+.4) w.append([[.42,.42],[-.42,.42]]); b.append([[0],[.2]]); p.append(p[-1]+.4) w.append([[.1,0],[0,.1]]); b.append([[0],[.2]]); p.append(1)