def __phi_f(s):
    t = (s / 7.5)
    return (tf.exp(((- s) / 2)) * ((((((1 + (3.5156229 * (t ** 2))) + (3.0899424 * (t ** 4))) + (1.2067492 * (t ** 6))) + (0.2659732 * (t ** 8))) + (0.0360768 * (t ** 10))) + (0.0045813 * (t ** 12))))
def __phi_f(s):
    t = (s / 7.5)
    return (tf.exp(((- s) / 2)) * ((((((1 + (3.5156229 * (t ** 2))) + (3.0899424 * (t ** 4))) + (1.2067492 * (t ** 6))) + (0.2659732 * (t ** 8))) + (0.0360768 * (t ** 10))) + (0.0045813 * (t ** 12))))