【C/C++】实现牛顿迭代

#include<bits/stdc++.h> 
using namespace std;


/*(x+2)^2 +1
    -2(x-1)^2+7

*/
double f(double x){
    return 4-x- pow(2,x);
}
double df(double x){
    return -1 - pow(2,x)*log(2);
}

//二分法
void binary_search(double l,double r,double e){
    
    double mid = (l+r)/2;
    int manN = 1000;
    int k = 1;
    int flag  = 0;
    while(1){
        mid = (l+r)/2;
        if(fabs(f(mid)) < e){
            flag = 1;
            break;
        }
        if(k>=manN){
            flag = 0;
            break;
        }
        if(f(l)*f(mid)<0){
            r = mid;
        }else if(f(mid)*f(r)<0){
            l = mid;
        }
        k++;
    }
    if(flag){
        printf("二分次数是：%d,解为：%.8lf
",k,mid);
    }
}
 
void NewTon(double x0,double e,int N){
    //牛顿法求根，起始点x0开始
    //N是最大迭代次数
    int flag = 0;  //1是奇异 2是找到了 3是失败 
    double x1,result;
    int k = 1; 
    while(1){
        if(df(x0) == 0){
            flag = 1;
            break;
        }
        x1 = x0 - f(x0)/df(x0);
        if(fabs(x1-x0) < e){
            result = x1;
            flag = 2;
            break;
        }
        if(k == N){
            flag = 3;
            break;
        }
        k++;
        //printf("%lf
",x0);
        x0 = x1; 
        
    }
    if(flag == 2){
        printf("找到了，并且迭代次数是：%d，根为：%.8lf
",k,result);
    }else if(flag == 1){
        printf("函数不可导");
    }else if(flag == 3){
        printf("超出局部收敛范围，迭代失败！
");
    }else{
        printf("return!");
    }
    return;
}
int main(){
    
//    double x0;
//    double e;
//    int N = 100;
//    //while(1){
//        printf("输入起始点、精度、最大迭代次数：");
//        cin>>x0>>e>>N;
//        NewTon(x0,e,N);        
//    
//
//    printf("-------------
");
//    printf("请输入二分法左右区间、精度：");
//    double l,r,e1; 
//    cin>>l>>r>>e1;
//    binary_search(l,r,e1);
    double x = 1.38616943;
    printf("%.10lf",f(x));
    
}