Newton_Raphson法求解非线性方程

//用Newton_Raphson法求解非线性方程
#include
#include
#include

using namespace std;

class raphson
{
private:
 int iteration;
 double eps, error, f, df, x_new, x_old;
 double pi, sigma, epsilon, h, T_a, T_w, D, I_sq_R;

public:
 raphson()
 {
  iteration = 0;
  pi = 3.14159;
  sigma = 5.67e-8;
  epsilon = 0.8;
  h = 25;
  T_a = 298;
  T_w = 298;
  D = 0.12;
  I_sq_R = 150;
 }
 void solution();
 double function(double x)
 {
  f = pi * D * (h * (x - T_a) + epsilon * sigma * (pow(x, 4) - pow(T_w, 4))) - I_sq_R;
  return f;
 }
 double deriv_function(double y)
 {
  df = pi * D * (h + 4 * epsilon * sigma * pow(y, 3));
  return df;
 }
};

void main()
{
 raphson nonlinear;
 nonlinear.solution();
}

void raphson::solution()
{
 cout << "\n输入初始估值：";
 cin >> x_old;
 cout << "\n输入公差：";
 cin >> eps;
 if (fabs(function(x_old)) < eps)
 {
  cout << "\n解是：" << x_old << endl;
  exit(0);
 }
 do
 {
  iteration++;
  x_new = x_old - function(x_old) / deriv_function(x_old);
  error = fabs(function(x_new));
  x_old = x_new;
 }while (error >= eps);
 cout << "\n解是：" << x_new << endl;
 cout << "\n收敛于" << iteration << "次迭代" << endl;
}