用二分法求方程的近似解

 

#include<cstdio>
#include<cstring>
#include<iostream>
#include<string>
#include<algorithm>
#include<cmath>
using namespace std;
//lnx + 2x - 6 = 0
//x=3 >0
//x=2 <0

double eps=1e-6;

int sgn(double x)
{
        if(x<-eps)
                return -1;
        else
                return x>eps;
}

int main()
{
        double x1=2, x2=3;
        while(sgn(x1-x2))
        {
                double x=(x1+x2)/2;
                cout<<x<<endl;
                int si=sgn(log(x)+2*x-6);
                if(si>0)
                        x2=x;
                else if(si<0)
                        x1=x;
                else//==0
                {
                        x1=x;
                        break;
                }
        }
        cout<<x1<<endl;


    return 0;
}