gammln.cpp

这是数学计算上常用的计算方法

#include <cmath>
#include "nr.h"
using namespace std;

DP NR::gammln(const DP xx)
{
	int j;
	DP x,y,tmp,ser;
	static const DP cof[6]={76.18009172947146,-86.50532032941677,
		24.01409824083091,-1.231739572450155,0.1208650973866179e-2,
		-0.5395239384953e-5};

	y=x=xx;
	tmp=x+5.5;
	tmp -= (x+0.5)*log(tmp);
	ser=1.000000000190015;
	for (j=0;j<6;j++) ser += cof[j]/++y;
	return -tmp+log(2.5066282746310005*ser/x);
}