数值积分之Simpson 1/3法则

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//实现Simpson 1/3法则
#include <iostream>
#include <math.h>

using namespace std;

class simpson
{
private:
 int n, k;
 double a, b, f, half_interval, integral, interval, sum_even_terms;
 double sum_odd_terms, x;

public:
 double func(double t)
 {
  f = 2e3 * log(1e5 / (1e5 - 2e3 * t)) - 10 * t;
  return f;
 }
 void integration();
};

void main()
{
 simpson simp;
 simp.integration();
}

void simpson::integration()
{
 cout << "\n输入上限和下限：";
 cin >> b >> a;
 cout << "\n输入你要使用simpson法则的数目（即等分数）：";
 cin >> n;
 interval = (b - a) / n;
 half_interval = interval / 2.0;
 sum_even_terms  = 0.0;
 sum_odd_terms = 0.0;
 for (k = 1; k < n; k++)
 {
  x = a + k * interval;
  sum_even_terms += func(x);
  sum_odd_terms += func(x + half_interval);
 }
 integral = (2.0 * sum_even_terms + 4.0 * sum_odd_terms - func(a) + func(b)) * half_interval / 3.0;
 cout << endl << "积分值 = " << integral << endl;
}

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