數值積分之Simpson 3/8法則

//實現Simpson 3/8法則
#include <iostream>
#include <math.h>

using namespace std;

class simpson2
{
private:
 int n, k;
 double a, b, f, integral, interval, one_third_interval;
 double sum_term1, sum_term2, sum_term3, x;

public:
 double func(double x)
 {
  f = (5.093e-5 * exp(2 * x)) / pow((1 + x * x), 2);
  return f;
 }
 void integration();
};

void main()
{
 simpson2 simp2;
 simp2.integration();
}

void simpson2::integration()
{
 cout << "\n輸入上限和下限：";
 cin >> b >> a;
 cout << endl << "\n輸入你要使用simpson 3/8法則的數目（即等分數）：";
 cin >> n;
 interval = (b - a) / n;
 one_third_interval = interval / 3.0;
 sum_term1 = 0.0;
 sum_term2 = 0.0;
 sum_term3 = 0.0;
 for (k = 1; k < n; k++)
 {
  x = a + k * interval;
  sum_term1 += func(x);
  sum_term2 += func(x + one_third_interval);
  sum_term3 += func(x + 2 * one_third_interval);
 }
 integral = (2 * sum_term1 + 3 * sum_term2 + 3 * sum_term3 - func(a) + func(b)) * (3 * one_third_interval / 8);
 cout << endl << "積分值 = " << integral << endl;
}