replace cdfNormal function in stats extension

gistfile1.txt

	//Cumulative Distribution Function of the Normal(0,1) distribution.
	//based on "A Note on Approximating the Normal Distribution Function", K. M. Aludaat and M. T. Alodat, Applied Mathematical Sciences 2008
	//Better is Abramowitz and Stegun;" Handbook of Mathematical Functions." 1964,(formula: 26.2.17) as implemented below
	//var cdfconst = Math.sqrt(Math.PI/8);
	
	math.normalCDF = function(z)
	{
	var p = 0.2316419;
	var a1=0.319381530;
	var a2=-0.356563782;
	var a3=1.781477937;
	var a4=-1.821255978;
	var a5= 1.330274429;
	
		var t = 1/(1+p*z);
		//return 0.5+0.5*Math.sqrt(1-Math.exp(-cdfconst*z*z));
		return 1-math.pdfNormal(z,0,1)*(a1*t+a2*Math.pow(t,2)+a3*Math.pow(t,3)+a4*Math.pow(t,4)+a5*Math.pow(t,5));
	}

	new funcObj('cdfNormal',[TNum],TNum,math.normalCDF);