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std::expone...distribution(3) C++ Standard Libarystd::expone...distribution(3) NAME std::exponential_distribution - std::exponential_distribution Synopsis Defined in header <random> template< class RealType = double > (since C++11) class exponential_distribution; Produces random non-negative floating-point values \(\small x\)x, distributed according to probability density function: \(\small P(x|\lambda) = \lambda e^{-\lambda x}\)P(x|) = e-x The value obtained is the time/distance until the next random event if random events occur at constant rate \(\small\lambda\) per unit of time/distance. For example, this distribution describes the time between the clicks of a Geiger counter or the distance between point mutations in a DNA strand. This is the continuous counterpart of std::geometric_distribution. std::exponential_distribution satisfies 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 lambda returns the lambda distribution parameter (rate of events) (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) Notes Some implementations may occasionally return infinity if RealType is float. This is LWG issue 2524. Example // Run this code #include <iostream> #include <iomanip> #include <random> #include <string> #include <map> int main() { std::random_device rd; std::mt19937 gen(rd()); // if particles decay once per second on average, // how much time, in seconds, until the next one? std::exponential_distribution<> d(1); std::map<int, int> hist; for(int n=0; n<10000; ++n) { ++hist[2*d(gen)]; } for(auto p : hist) { std::cout << std::fixed << std::setprecision(1) << p.first/2.0 << '-' << (p.first+1)/2.0 << ' ' << std::string(p.second/200, '*') << '\n'; } } Possible output: 0.0-0.5 ******************* 0.5-1.0 *********** 1.0-1.5 ******* 1.5-2.0 **** 2.0-2.5 ** 2.5-3.0 * 3.0-3.5 3.5-4.0 External links Weisstein, Eric W. "Exponential Distribution." From MathWorld--A Wolfram Web Resource. http://cppreference.com 2022.07.31 std::expone...distribution(3)
NAME | Synopsis | Template parameters | Member types | Member functions | Generation | Characteristics | Non-member functions | Notes | Example | Possible output: | External links
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