trapzd.cpp

龙贝格积分

#include "stdafx.h"
#define FUNC(x) ((*func)(x))

double trapzd(double (*func)(double),double a,double b,int n)
{
	double x,tnm,sum,del;
	static double s;
	static int it;
	int j;

	if (n == 1) {
		it=1;
		return (s=0.5*(b-a)*(FUNC(a)+FUNC(b)));
	} else {
		tnm=it;
		del=(b-a)/tnm;
		x=a+0.5*del;
		for (sum=0.0,j=1;j<=it;j++,x+=del) sum += FUNC(x);
		it *= 2;
		s=0.5*(s+(b-a)*sum/tnm);
		return s;
	}
}