1//===----------------------------------------------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// REQUIRES: long_tests
10
11// <random>
12
13// template<class RealType = double>
14// class normal_distribution
15
16// template<class _URNG> result_type operator()(_URNG& g, const param_type& parm);
17
18#include <random>
19#include <cassert>
20#include <cmath>
21#include <cstddef>
22#include <numeric>
23#include <vector>
24
25#include "test_macros.h"
26
27template <class T>
28inline
29T
30sqr(T x)
31{
32 return x * x;
33}
34
35int main(int, char**)
36{
37 {
38 typedef std::normal_distribution<> D;
39 typedef D::param_type P;
40 typedef std::minstd_rand G;
41 G g;
42 D d(5, 4);
43 P p(50, .5);
44 const int N = 1000000;
45 std::vector<D::result_type> u;
46 for (int i = 0; i < N; ++i)
47 u.push_back(d(g, p));
48 double mean = std::accumulate(u.begin(), u.end(), 0.0) / u.size();
49 double var = 0;
50 double skew = 0;
51 double kurtosis = 0;
52 for (std::size_t i = 0; i < u.size(); ++i)
53 {
54 double dbl = (u[i] - mean);
55 double d2 = sqr(dbl);
56 var += d2;
57 skew += dbl * d2;
58 kurtosis += d2 * d2;
59 }
60 var /= u.size();
61 double dev = std::sqrt(x: var);
62 skew /= u.size() * dev * var;
63 kurtosis /= u.size() * var * var;
64 kurtosis -= 3;
65 double x_mean = p.mean();
66 double x_var = sqr(p.stddev());
67 double x_skew = 0;
68 double x_kurtosis = 0;
69 assert(std::abs((mean - x_mean) / x_mean) < 0.01);
70 assert(std::abs((var - x_var) / x_var) < 0.01);
71 assert(std::abs(skew - x_skew) < 0.01);
72 assert(std::abs(kurtosis - x_kurtosis) < 0.01);
73 }
74
75 return 0;
76}
77

source code of libcxx/test/std/numerics/rand/rand.dist/rand.dist.norm/rand.dist.norm.normal/eval_param.pass.cpp