def sigma(self, alpha):
    a1 = ((- MAV.M) * (alpha - MAV.alpha0))
    a2 = (MAV.M * (alpha + MAV.alpha0))
    sigma_alpha = (((1 + np.exp(a1)) + np.exp(a2)) / ((1 + np.exp(a1)) * (1 + np.exp(a2))))
    return sigma_alpha
def sigma(self, alpha):
    a1 = ((- MAV.M) * (alpha - MAV.alpha0))
    a2 = (MAV.M * (alpha + MAV.alpha0))
    sigma_alpha = (((1 + np.exp(a1)) + np.exp(a2)) / ((1 + np.exp(a1)) * (1 + np.exp(a2))))
    return sigma_alpha