using System;

namespace BrazilTimestampReconstruction
{
	/// <summary>
	/// Returns the incomplete gamma function Q(a, x) evaluated by its continued fraction representation
	/// as gammcf. Also returns ln\Gamma(a) as gln.
	/// </summary>
	public class Gcf
	{
		private double gammcf, gln;
		public double Gammcf
		{
			get{return gammcf;}
		}
		public double Gln
		{
			get{return gln;}
		}
		public Gcf()
		{
		}
		private int ITMAX = 100;
        private double EPS = 3.0e-7;
        private double FPMIN = 1.0e-30;
		public void gcf(double a, double x)
		{
			Gammln gam = new Gammln();	
	        int i;
	        double an,b,c,d,del,h;

	        gln=gam.gammln(a);
	        b=x+1.0-a;
	        c=1.0/FPMIN;
	        d=1.0/b;
	        h=d;
	        for (i=1;i<=ITMAX;i++) 
			{
		        an = -i*(i-a);
		        b += 2.0;
		        d=an*d+b;
		        if (Math.Abs(d) < FPMIN) d=FPMIN;
		        c=b+an/c;
		        if (Math.Abs(c) < FPMIN) c=FPMIN;
		        d=1.0/d;
		        del=d*c;
		        h *= del;
		        if (Math.Abs(del-1.0) < EPS) break;
	        }
			if (i > ITMAX) try{throw new Exception();}
						   catch (Exception)
						   {
							   
						   } 
	        gammcf=Math.Exp(-x+a*Math.Log(x)-gln)*h;
		}
	}
}