The same equations were used to generate this image as well.  The only difference is the starting point.  Instead of expanding from the center of the distortion field, the starting point is displaced a little bit towards the bottom.  This highlights a number of different things. First while the equations are symmetric, the resulting image is decidedly asymmetric.  If you follow the lines to the right vs. the ones to the left, you can see that the paths have decidedly different curves.