newton.cpp

计算方法经典算法(弦截法二分法牛顿迭代法龙贝格算法)

#include<iostream.h>
#include<math.h>
#include<stdlib.h>

double f(double x)
{
	return 2*x*x+7*x-15;
}
double df(double x)//求f（x）的导数
{
	return 4*x+7;
}


void Newton(double x0,double l)//根的初始近似值和所需精度
{
	double x[30];
	x[0]=x0;
	for(int k=0;k<30;k++)
	{
		x[k+1]=x[k]-(f(x[k])/df(x[k]));
		if(fabs(x[k-1]-x[k])<l)
		{	cout<<"data="<<x[k+1]<<endl;exit(1);}
	}
	cout<<"not found root!";
}

void main()
{
	cout<<"please input x0,l:"<<endl;
	double x0,l;
	cin>>x0>>l;
	Newton(x0,l);
}