Martin’s doileys

An iteration due to artist mathematician [1] Barry Martin produces intricate doiley-like patterns by iterating a simple mathematical function. I ran across this via [2].

The images produced are sensitive to small changes in the starting parameters x and y, as well as to the parameters a, b, and c.

Here are three examples:

And here’s the Python code that was used to make these plots.

    import matplotlib.pyplot as plt
    from numpy import sign, empty

    def make_plot(x, y, a, b, c, filename, N=20000):
        xs = empty(N)
        ys = empty(N)
        for n in range(N):
            x, y = y - sign(x)*abs(b*x - c)**0.5, a - x
            xs[n] = x
            ys[n] = y
        plt.scatter(xs, ys, c='k', marker='.', s = 1, alpha=0.5)
        plt.axes().set_aspect(1)
        plt.axis('off')
        plt.savefig(filename)
        plt.close()

    make_plot(5, 5, 30.5, 2.5, 2.5, "doiley1.png")
    make_plot(5, 6, 30, 3, 3, "doiley2.png")
    make_plot(3, 4, 5, 6, 7, "doiley3.png")

[1] Tom Crilly identified Martin as an artist in [2] and I repeated this error. Barry Martin informed me of the error in the comments below.

[2] Desert Island Theorems: My Magnificent Seven by Tony Crilly. The Mathematical Gazette, Mar., 2001, Vol. 85, No. 502 (Mar., 2001), pp. 2-12