In mathematics, a Lissajous curve ( /ˈlɪsəʒuː/ and /ˈbaʊdɪtʃ/), also known as Lissajous figure or Bowditch curve, is the graph of a system of parametric equations which describe complex harmonic motion. […] The appearance of the figure is highly sensitive to the ratio a/b. For a ratio of 1, the figure is an ellipse, with special cases including circles (A = B, δ = π/2 radians) and lines (δ = 0). Another simple Lissajous figure is the parabola (a/b = 2, δ = π/2). Other ratios produce more complicated curves, which are closed only if a/b is rational. The visual form of these curves is often suggestive of a three-dimensional knot […].