1 //===----------------------------------------------------------------------===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is dual licensed under the MIT and the University of Illinois Open 6 // Source Licenses. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 10 // <random> 11 12 // template<class RealType = double> 13 // class normal_distribution 14 15 // template<class _URNG> result_type operator()(_URNG& g); 16 17 #include <random> 18 #include <cassert> 19 #include <vector> 20 #include <numeric> 21 22 template <class T> 23 inline 24 T sqr(T x)25sqr(T x) 26 { 27 return x * x; 28 } 29 main()30int main() 31 { 32 { 33 typedef std::normal_distribution<> D; 34 typedef D::param_type P; 35 typedef std::minstd_rand G; 36 G g; 37 D d(5, 4); 38 const int N = 1000000; 39 std::vector<D::result_type> u; 40 for (int i = 0; i < N; ++i) 41 u.push_back(d(g)); 42 double mean = std::accumulate(u.begin(), u.end(), 0.0) / u.size(); 43 double var = 0; 44 double skew = 0; 45 double kurtosis = 0; 46 for (int i = 0; i < u.size(); ++i) 47 { 48 double d = (u[i] - mean); 49 double d2 = sqr(d); 50 var += d2; 51 skew += d * d2; 52 kurtosis += d2 * d2; 53 } 54 var /= u.size(); 55 double dev = std::sqrt(var); 56 skew /= u.size() * dev * var; 57 kurtosis /= u.size() * var * var; 58 kurtosis -= 3; 59 double x_mean = d.mean(); 60 double x_var = sqr(d.stddev()); 61 double x_skew = 0; 62 double x_kurtosis = 0; 63 assert(std::abs((mean - x_mean) / x_mean) < 0.01); 64 assert(std::abs((var - x_var) / x_var) < 0.01); 65 assert(std::abs(skew - x_skew) < 0.01); 66 assert(std::abs(kurtosis - x_kurtosis) < 0.01); 67 } 68 } 69