def __phi_g(s):
    t = (s / 7.5)
    return (tf.sqrt((2 / s)) * ((((((((0.39894228 + (0.01328592 * (t ** (- 1)))) + (0.00225319 * (t ** (- 2)))) - (0.00157565 * (t ** (- 3)))) + (0.0091628 * (t ** (- 4)))) - (0.02057706 * (t ** (- 5)))) + (0.02635537 * (t ** (- 6)))) - (0.01647633 * (t ** (- 7)))) + (0.00392377 * (t ** (- 8)))))
def __phi_g(s):
    t = (s / 7.5)
    return (tf.sqrt((2 / s)) * ((((((((0.39894228 + (0.01328592 * (t ** (- 1)))) + (0.00225319 * (t ** (- 2)))) - (0.00157565 * (t ** (- 3)))) + (0.0091628 * (t ** (- 4)))) - (0.02057706 * (t ** (- 5)))) + (0.02635537 * (t ** (- 6)))) - (0.01647633 * (t ** (- 7)))) + (0.00392377 * (t ** (- 8)))))