'Returns the frequency of the MA roots.
This is the solution, x, to z = abs(z)*exp(2j*np.pi*x) where z are the
roots.'

@cache_readonly
def mafreq(self):

    z = self.maroots
    if (not z.size):
        return
    return (np.arctan2(z.imag, z.real) / (2 * pi))
