using static System.Math;
public static partial class math{

public static double erf(double x){
/* single precision error function (Abramowitz and Stegun) */
	if(x<0) return -erf(-x);
	double[] a =
	{0.254829592,-0.284496736,1.421413741,-1.453152027,1.061405429};
	double t=1/(1+0.3275911*x);
	double sum=t*(a[0]+t*(a[1]+t*(a[2]+t*(a[3]+t*a[4]))));
	return 1.0-sum*Exp(-x*x);
}//erf

public static double gamma(double x){
/* single precision gamma function (Wikipedia) */
	if(x<0)return PI/Sin(PI*x)/gamma(-x+1);
	if(x<10)return gamma(x+1)/x; /* move argument up */
	double a=1.0/12, b=1.0/12;
	double lngamma=x*Log(x)-x+0.5*Log(2*PI/x)+a/(x+1)+b/(x+1)/(x+2);
	return Exp(lngamma);
}//gamma

}//math