定积分（任意函数求积分）

 1 #define eps 1e-8
 2
 3 double fun(double x) {
 4     /*函数部分*/
 5 }
 6
 7 double Definite_Integral(double a, double b) {
 8     double p = eps + 1.0;
 9     double t, h = b - a, t1 = (fun(a) + fun(b)) * h / 2;
10     while(p >= eps) {
11         double s = 0;
12         for(double k = a + h / 2; k <= b; k += h)s += fun(k);
13         t = t1 / 2 + h * s / 2;
14         p = fabs(t - t1);
15         t1 = t;
16         h /= 2;
17     }
18     return t;
19 }

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