gammln.c

Numerical Recipes 是国际公认的高水平的、关于数值计算的书

#include <math.h>

float gammln(xx)
float xx;
{
	double x,tmp,ser;
	static double cof[6]={76.18009173,-86.50532033,24.01409822,
		-1.231739516,0.120858003e-2,-0.536382e-5};
	int j;

	x=xx-1.0;
	tmp=x+5.5;
	tmp -= (x+0.5)*log(tmp);
	ser=1.0;
	for (j=0;j<=5;j++) {
		x += 1.0;
		ser += cof[j]/x;
	}
	return -tmp+log(2.50662827465*ser);
}