private static DoubleDouble Erfc_ContinuedFraction(DoubleDouble x)
{
DoubleDouble x2 = x * x;
double aa = 1.0;
DoubleDouble bb = x2 + 0.5;
DoubleDouble D = 1.0 / bb;
DoubleDouble Df = aa / bb;
DoubleDouble f = Df;
for (int k = 1; k < 100; k++)
{
DoubleDouble f_old = f;
aa = -k * (k - 0.5);
bb += 2.0;
D = 1.0 / (bb + aa * D);
Df = (bb * D - 1.0) * Df;
f += Df;
if (f == f_old)
{
DoubleDouble e = DoubleDouble.Exp(-x2);
DoubleDouble g = x / DoubleDouble.Sqrt(DoubleDouble.Pi);
return(e * f * g);
}
}
throw new InvalidOperationException();
}
private static DoubleDouble Erf_Series(DoubleDouble x)
{
DoubleDouble mx2 = -(x * x);
DoubleDouble t = DoubleDouble.One;
DoubleDouble f = t;
for (int k = 1; k < 100; k++)
{
DoubleDouble f_old = f;
t *= mx2 / k;
f += t / (2 * k + 1);
if (f == f_old)
{
return((2.0 / DoubleDouble.Sqrt(DoubleDouble.Pi)) * x * f);
}
}
throw new InvalidOperationException();
}
