/// <summary>
/// 분포의 로그 확률 밀도
/// </summary>
/// <param name="x"></param>
/// <returns></returns>
public double DensityLn(double x)
{
// TODO JVG we can probably do a better job for Cauchy special case
if (double.IsPositiveInfinity(_dof))
{
return(Normal.DensityLn(_location, _scale, x));
}
var d = (x - _location) / _scale;
return(SpecialFunctions.GammaLn((_dof + 1.0) / 2.0)
- (0.5 * ((_dof + 1.0) * Math.Log(1.0 + (d * d / _dof))))
- SpecialFunctions.GammaLn(_dof / 2.0)
- (0.5 * Math.Log(_dof * Math.PI)) - Math.Log(_scale));
}