数值积分之Simpson 1/3法则

//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;

}