问使用其他成员函数的C++成员函数

EN

#include <vector>
#include <cmath>

using namespace std   

class CDS
{
public:
    CDS(); 
    CDS(double notional, vector<double> pay_times, vector<double> intensity);
    ~CDS(); 


 double m_notional; 
 vector<double> m_paytimes;
 vector<double> m_intensity;

 double intensity_func(double);

 double big_gamma(double);

};

#include <vector>
#include <random>
#include <cmath>

#include "CDS.h"

double CDS::intensity_func(double t)
{
    vector<double> x = this->m_intensity;
    vector<double> y = this->m_paytimes;
    if(t >= y.back() || t< y.front())
    {
        return 0;
    }

    else
    {
        int d=index_beta(y, t) - 1;
        double result = x.at(d) + (x.at(d+1) - x.at(d))*(t - y.at(d))/ (y.at(d+1) - y.at(d));
        return result;
    }

double simple_integration ( double (*fct)(double),double a, double b) 
{
       //Compute the integral of a (continuous) function on [a;b]
       //Simpson's rule is used
       return (b-a)*(fct(a)+fct(b)+4*fct((a+b)/2))/6;
};


double integration(double (*fct)(double),double a, double b, double N) 
{
       //The integral is computed using the simple_integration function
       double sum = 0;
       double h = (b-a)/N;
       for(double x = a; x<b ; x = x+h) {
             sum += simple_integration(fct,x,x+h);
       }
       return sum;
};

int index_beta(vector<double> x, double tau)
{
    // The vector x is sorted in increasing order and tau is a double


    if(tau < x.back())
    {
        vector<double>::iterator it = x.begin();
        int n=0;

        while (*it < tau)
        {
            ++ it;
            ++n; // or n++;
        }
        return n;
    }

    else
    {
        return x.size();
    }


};

double CDS::big_gamma(double t)
{
    return  integration(this->intensity, 0, t);
};