[EQ] r(\phi) = \left[ \left| \frac{\cos\left(\frac{m\phi}{4}\right)}{a} \right|^{n_2} + \left| \frac{\sin\left(\frac{m\phi}{4}\right)}{b} \right|^{n_3} \right]^{-\frac{1}{n_1}} [/EQ]