c++解一元三次方程

求解一元三次方程组

转自：http://blog.youkuaiyun.com/u012221917/article/details/17175793

float f(float w_f, float x_f, float y_f, float z_f, double sol_f)//当根为x时，用来求f(x)的值
{
    double f_result = w_f*pow(sol_f, 3) + x_f*pow(sol_f, 2) + y_f*sol_f + z_f;
    //cout<<"f_result is "<<f_result<<endl; //调试时用
    return f_result;
}

float f1(float w_f1, float x_f1, float y_f1, float z_f1, double sol_f1) //当根为x时，用来求f'(x)的值
{
    double f1_result = 3 * w_f1*pow(sol_f1, 2) + 2 * x_f1*sol_f1 + y_f1;
    //cout<<"f1_result is "<<f1_result<<endl;//调试时用
    return f1_result;
}

float get_solution(float w, float x, float y, float z, double sol) //求根函数，调用了上面两个函数
{
    double value, tmp;

    value = sol;
    do //使用了x1=x0-f(x0)/f'(x0)，不断循环逼近
    {
        tmp = f(w, x, y, z, value);
        value = value - tmp / f1(w, x, y, z, value);

        //cout<<"funciont_value is "<<tmp<<";value is "<<value<<endl;//调试时用
    } while (fabs(tmp) >= 1e-5);//当式子的值与0的绝对值小于1e-5时就认为取到了值

    return value;
}