数值计算：
这种积分的计算方法很好，学习一下！
代码：
1 #include <iostream> 2 #include <cmath> 3 using namespace std; 4 const double eps = 10e-5; 5 6 double func(double a, double b, double x) 7 { 8 double r = a * exp(- x*x) + b * sqrt(x); 9 return r*r; 10 } 11 12 double integrate(double a, double b, double h) 13 { 14 unsigned long steps = 1, it = 1; 15 double V = h*(func(a,b,0)+func(a,b,h))/2.0; 16 double Vold; 17 do 18 { 19 double tmp = 0; 20 steps *= 2; 21 for (unsigned long i = 1; i < steps; i += 2) 22 { 23 tmp += func(a, b, (h * i) / steps); 24 } 25 Vold = V; 26 V = (V / 2.0) + ((tmp * h) / steps); 27 } 28 while (fabs(V - Vold) > eps); 29 return V; 30 } 31 32 int main() 33 { 34 double V, a, b, h; 35 double e_min = 2e100; 36 int i_min = 0; 37 int N; 38 cin >> V >> N; 39 V /= 3.14159265358979; 40 for (int i = 0; i < N; i++) 41 { 42 cin >> a >> b >> h; 43 double e = fabs(V -integrate(a, b, h)); 44 if (e < e_min) 45 { 46 e_min = e; 47 i_min = i; 48 } 49 } 50 cout << i_min << endl; 51 return 0; 52 }