define phi(x) {
    t = 0
    s = x
    b = x
    q = x * x
    i = 1
    while (s != t) {s = (t = s) + (b = b * (q / (i = i + 2)))}
    const = 0.5 * l(8 * a(1))
    0.5 + s * e(-0.5 * q - const)}
phi(1)