循环不适用于割线方法

我为找到方程的根而编写的程序已接近完成，但我遇到了一个小问题。我用来将速度和角度的变化值分配给方程的嵌套循环不起作用。无论是在循环中的某个地方，还是在调用 fx 割线的某个地方，我都错过了一个错误。它一直为我提供相同的根、迭代次数和 f（x） 数字。如果有人能帮助我找到我的错误，我将不胜感激:)

#include<iostream>
#include<cmath>
#include<iomanip>
#include<fstream>
using namespace std;
// Declaration of functions used
void secant(double, double, double, double, double, double, double, double, double&, int& );
double fx( double, double, double, double, double, double, double);
const double tol=0.0001;
// Tolerance for convergence
const int max_iter=50; // Maximum iterations allowed
// main program
int main()
{
    int iteration;  // Number of iterations    
    double kr, uc, q, b, radians; 
    double x0, x1;  // Starting values for x   
    double root;    // Root found by secant method
    const double PI = 4.0*atan(1.0);
    ifstream datain ("shuttle.txt");
    ofstream dataout ("results.txt");
    datain >> kr >> uc >> q >> b;
    int velocity = 16000;
    double angle =10;
    x0= 1000;
    x1 = 200;
    for (int velocity = 16000; velocity <= 17500; velocity += 500)
    {   
        for (int angle = 10; angle <= 70; angle += 15)
        { 
            radians= angle * PI/180  ; 
            cout << velocity << endl; 
            cout << radians << endl;   
            cout << angle << endl;                  
            secant (radians, velocity, kr, uc, q, b, x0, x1, root, iteration);      
        }
    } 
    system("pause");
}
// Definition of function "secant"
// Receives a, b, c, d and x0 values from main program
// Returns root and the iterations required
void secant(double radians,double velocity, double kr, double uc, double q, double b, double x0, double x1, double& root, int& iteration)
{    
    double xnminus1, xnplus1, xn; // Local variables
    iteration=0;    // Initialize iterations    
    xnminus1=x0;
    xn=x1;  
    do  
    {   
        ++iteration; 
        xnplus1 = xn - fx(radians, velocity, kr, uc, q, b, xn)*(xn-xnminus1)/(fx(radians, velocity, kr, uc, q, b, xn)-fx(radians, velocity, kr, uc, q, b, xnminus1)); 
        cout<<"x"<<iteration+1<<" = "<<xnplus1<<endl;  
        xnminus1 = xn;
        xn=xnplus1; 
    } while ((fabs(fx(radians, velocity, kr, uc, q, b, xnplus1)) >= tol )&& (iteration < max_iter)); 
    root=xnplus1;  
    cout<<"nThe root is = "<<root<<endl; 
    cout<<"The number of iterations was = "<<iteration<<endl; 
    cout<<"The value of f(x) at the root = "<<fx(radians, velocity, kr, uc, q, b, root)<<endl<<endl;
}
// Defines "fx" 
double fx(double radians,double velocity, double kr, double uc, double q, double b, double ts)
{
    return kr * pow(ts,4.0) + uc * ts - q - pow(velocity / b, 2.0) * sin(radians);
}