xianjie.cpp

用双点弦截法计算f(x)=0

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

long double ab(long double s)
{
	if(s<0)
		s=-s;
	return s;
}

long double f(long double s)
{
	long double m;
	m=cos(2*s)-9.0/4*s;
	return m;
}

void main()
{
	long double x=0.0,y=1.0,c=0.0000000000001,u,v,z,w;
	u=f(x);
	int k=0;
	cout<<k<<"\t"<<setprecision(10)<<x<<"\t"<<setprecision(10)<<u<<endl;
	v=f(y);
	k++;
	cout<<k<<"\t"<<setprecision(10)<<y<<"\t"<<setprecision(10)<<v<<endl;
	do{
		z=y-(y-x)*v/(v-u);
		w=f(z);
		k++;
		cout<<k<<"\t"<<setprecision(10)<<z<<"\t"<<setprecision(10)<<w<<endl;
		x=y;
		y=z;
		u=v;
		v=w;
	}while(ab(w)>=c);
}