cdf method
Gives the normal cumulative distribution function.
Approximation within 7.5E-8 (Abramowitz 26.2.17) of the cumulative probability.
Implementation
num cdf(num x) {
final z0 = (x - mean) / standardDeviation,
z = z0.abs(),
t = 1 / (1 + _p * z),
tps = [for (var i = 0; i < _nb; i++) math.pow(t, i + 1)],
c = _standardDensity(z) *
[for (var i = 0; i < _nb; i++) _b[i] * tps[i]]
.fold(0, (a, b) => a + b);
return z0 < 0 ? c : 1 - c;
}