rtnewt.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::rtnewt(void funcd(const DP, DP &, DP &), const DP x1, const DP x2,
	const DP xacc)
{
	const int JMAX=20;
	int j;
	DP df,dx,f,rtn;

	rtn=0.5*(x1+x2);
	for (j=0;j<JMAX;j++) {
		funcd(rtn,f,df);
		dx=f/df;
		rtn -= dx;
		if ((x1-rtn)*(rtn-x2) < 0.0)
			nrerror("Jumped out of brackets in rtnewt");
		if (fabs(dx) < xacc) return rtn;
	}
	nrerror("Maximum number of iterations exceeded in rtnewt");
	return 0.0;
}