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 piecewise_linear_distribution 14 15 // template<class _URNG> result_type operator()(_URNG& g, const param_type& parm); 16 17 #include <random> 18 #include <vector> 19 #include <iterator> 20 #include <numeric> 21 #include <cassert> 22 23 template <class T> 24 inline 25 T 26 sqr(T x) 27 { 28 return x*x; 29 } 30 31 double 32 f(double x, double a, double m, double b, double c) 33 { 34 return a + m*(sqr(x) - sqr(b))/2 + c*(x-b); 35 } 36 37 int main() 38 { 39 { 40 typedef std::piecewise_linear_distribution<> D; 41 typedef D::param_type P; 42 typedef std::mt19937_64 G; 43 G g; 44 double b[] = {10, 14, 16, 17}; 45 double p[] = {25, 62.5, 12.5, 0}; 46 const size_t Np = sizeof(p) / sizeof(p[0]) - 1; 47 D d; 48 P pa(b, b+Np+1, p); 49 const int N = 1000000; 50 std::vector<D::result_type> u; 51 for (int i = 0; i < N; ++i) 52 { 53 D::result_type v = d(g, pa); 54 assert(10 <= v && v < 17); 55 u.push_back(v); 56 } 57 std::sort(u.begin(), u.end()); 58 int kp = -1; 59 double a; 60 double m; 61 double bk; 62 double c; 63 std::vector<double> areas(Np); 64 double S = 0; 65 for (int i = 0; i < areas.size(); ++i) 66 { 67 areas[i] = (p[i]+p[i+1])*(b[i+1]-b[i])/2; 68 S += areas[i]; 69 } 70 for (int i = 0; i < areas.size(); ++i) 71 areas[i] /= S; 72 for (int i = 0; i < Np+1; ++i) 73 p[i] /= S; 74 for (int i = 0; i < N; ++i) 75 { 76 int k = std::lower_bound(b, b+Np+1, u[i]) - b - 1; 77 if (k != kp) 78 { 79 a = 0; 80 for (int j = 0; j < k; ++j) 81 a += areas[j]; 82 m = (p[k+1] - p[k]) / (b[k+1] - b[k]); 83 bk = b[k]; 84 c = (b[k+1]*p[k] - b[k]*p[k+1]) / (b[k+1] - b[k]); 85 kp = k; 86 } 87 assert(std::abs(f(u[i], a, m, bk, c) - double(i)/N) < .001); 88 } 89 } 90 } 91
