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std::gamma_distribution(3) C++ Standard Libary std::gamma_distribution(3) NAME std::gamma_distribution - std::gamma_distribution Synopsis Defined in header <random> template< class RealType = double > (since C++11) class gamma_distribution; Produces random positive floating-point values x, distributed ac- cording to probability density function: \(\mathsf{p}(x\mid\alpha,\beta) = \frac{e^{-x/\beta} }{\beta^\alpha\cdot\Gamma(\alpha)}\cdot x^{\alpha-1} \)P(x|,) = e-x/ () x-1 where is known as the shape parameter and is known as the scale parameter. The shape parameter is sometimes denoted by the letter k and the scale parameter is sometimes denoted by the letter . For floating-point , the value obtained is the sum of independent exponentially distributed random variables, each of which has a mean of . std::gamma_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 alpha returns the distribution parameters beta (public member function) (C++11) 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 <iomanip> #include <iostream> #include <map> #include <random> #include <string> int main() { std::random_device rd; std::mt19937 gen(rd()); // A gamma distribution with alpha = 1, and beta = 2 // approximates an exponential distribution. std::gamma_distribution<> d(1, 2); std::map<int, int> hist; for (int n = 0; n != 10000; ++n) ++hist[2 * d(gen)]; for (auto const& [x, y] : hist) if (y / 100.0 > 0.5) std::cout << std::fixed << std::setprecision(1) << x / 2.0 << '-' << (x + 1) / 2.0 << ' ' << std::string(y / 100, '*') << '\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 **** 4.0-4.5 *** 4.5-5.0 ** 5.0-5.5 ** 5.5-6.0 * 6.0-6.5 * 6.5-7.0 7.0-7.5 7.5-8.0 External links Weisstein, Eric W. "Gamma Distribution." From MathWorld A Wolfram Web Resource. http://cppreference.com 2024.06.10 std::gamma_distribution(3)
NAME | Synopsis | Template parameters | Member types | Member functions | Generation | Characteristics | Non-member functions | Example | Possible output: | External links
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