public static double logBeta(double a, double b)
{
double corr, ans;
double p = JMath.min(a, b);
double q = JMath.max(a, b);
if (p <= 0.0)
{
ans = double.NaN;
}
else if (p >= 10.0)
{
corr = r9lgmc(p) + r9lgmc(q) - r9lgmc(p + q);
double temp = dlnrel(-p / (p + q));
ans = -0.5 * JMath.log(q) + 0.918938533204672741780329736406 + corr + (p - 0.5) * JMath.log(p / (p + q)) + q * temp;
}
else if (q >= 10.0)
{
corr = Sfun.r9lgmc(q) - r9lgmc(p + q);
ans = logGamma(p) + corr + p - p * JMath.log(p + q) + (q - 0.5) * dlnrel(-p / (p + q));
}
else
{
ans = JMath.log(gamma(p) * (gamma(q) / gamma(p + q)));
}
return(ans);
}
private static double dlnrel(double x)
{
double ans;
if (x <= -1.0)
{
ans = double.NaN;
}
else if (JMath.abs(x) <= 0.375)
{
ans = x * (1.0 - x * Sfun.csevl(x / .375, ALNRCS_COEF));
}
else
{
ans = JMath.log(1.0 + x);
}
return(ans);
}
internal override Symbolic PreEval(Symbolic x)
{
return(new Complex(Sfun.logGamma(x.ToComplex().Re)));
}
internal override Zahl f(Zahl x)
{
return(new Unexakt(Sfun.logGamma(x.unexakt().real)));
}
