r = 1.3 (slider from -5 to 5, step 0.1)
e = 22.7 (slider from 0 to 32, step 0.1)
a = CurveCartesian(((r * (1 - t / e)) * cos(t)), ((r * (1 - t / e)) * sin(t)), t / ((2 * π)), t, 0, e)