Eqn (7) from Greenhall2004

def greenhall_sw(t, alpha):
    """ Eqn (7) from Greenhall2004
    """
    alpha = int(alpha)
    if alpha == 2:
            return -np.abs(t)
    elif alpha == 1:
        if t == 0:
            return 0
        else:
            return pow(t, 2)*np.log(np.abs(t))
    elif alpha == 0:
        return np.abs(pow(t, 3))
    elif alpha == -1:
        if t == 0:
            return 0
        else:
            return pow(t, 4)*np.log(np.abs(t))
    elif alpha == -2:
        return np.abs(pow(t, 5))
    elif alpha == -3:
        if t == 0:
            return 0
        else:
            return pow(t, 6)*np.log(np.abs(t))
    elif alpha == -4:
        return np.abs(pow(t, 7))

    assert(0)