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std::piecew...istribution(3) C++ Standard Libary std::piecew...istribution(3) NAME std::piecewise_linear_distribution - std::piecewise_linear_distribution Synopsis Defined in header <random> template< class RealType = double > (since C++11) class piecewise_linear_distribution; std::piecewise_linear_distribution produces random floating-point numbers, which are distributed according to a linear probability density function within each of the several subintervals \(\small{[b_i, b_{i+1})}\)[b i, b i+1). The distribution is such that the probability density at each interval boundary is exactly the predefined value \(\small{p_i}\)p i. The probability density for any \(\small{ b_i \le x < b_{i+1} }\)b ix<b i+1 is \(\small{p_i\frac{b_{i+1}-x}{b_{i+1}-b_i} + p_{i+1}\frac{x- b_i}{b_{i+1}-b_i} }\)p i b i+1-x b i+1-b i + p i+1 x-b i b i+1-b i , where probability densities at interval boundaries \(\small{p_k}\)p k are calculated as \(\small{w_k/S}\)w k/S where \(\small{S}\)S is the sum of all \(\small{\frac{1}{2}(w_k + w_{k+1})(b_{k+1} - b_k)}\) 1 2 (w k+w k+1)(b k+1b k). The set of interval boundaries \(\small{b_i}\)b i and the set of weights at boundaries \(\small{w_i}\)w i are the parameters of this distribution. std::piecewise_linear_distribution satisfies all requirements of RandomNumberDistribution Template parameters RealType - The result type generated by the generator. The effect is undefined if this is not one of float, double, or long double. Member types Member type Definition result_type(C++11) RealType param_type(C++11) the type of the parameter set, see RandomNum- berDistribution. Member functions constructor constructs new distribution (C++11) (public member function) reset resets the internal state of the distribution (C++11) (public member function) Generation operator() generates the next random number in the distribution (C++11) (public member function) Characteristics intervals returns the distribution parameters densities (public member function) param gets or sets the distribution parameter object (C++11) (public member function) min returns the minimum potentially generated value (C++11) (public member function) max returns the maximum potentially generated value (C++11) (public member function) Non-member functions operator== operator!= compares two distribution objects (C++11) (function) (C++11)(removed in C++20) operator<< performs stream input and output on pseudo-random number operator>> distribution (C++11) (function template) Example // Run this code #include <iostream> #include <iomanip> #include <string> #include <map> #include <random> int main() { std::random_device rd; std::mt19937 gen{rd()}; // increase the probability from 0 to 5 // remain flat from 5 to 10 // decrease from 10 to 15 at the same rate std::vector<double> i{0, 5, 10, 15}; std::vector<double> w{0, 1, 1, 0}; std::piecewise_linear_distribution<> d{i.begin(), i.end(), w.be- gin()}; std::map<int, int> hist; for(int n=0; n<10000; ++n) { ++hist[d(gen)]; } for(auto p : hist) { std::cout << std::setw(2) << std::setfill('0') << p.first << ' ' << std::string(p.second/100,'*') << '\n'; } } Possible output: 00 * 01 *** 02 **** 03 ****** 04 ********* 05 ********* 06 ********* 07 ********** 08 ********* 09 ********** 10 ********* 11 ******* 12 **** 13 *** 14 * http://cppreference.com 2022.07.31 std::piecew...istribution(3)
NAME | Synopsis | Template parameters | Member types | Member functions | Generation | Characteristics | Non-member functions | Example | Possible output:
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