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std::poisson_distribution(3)   C++ Standard Libary  std::poisson_distribution(3)

NAME
     std::poisson_distribution - std::poisson_distribution

Synopsis
	Defined in header <random>
	template< class IntType = int >  (since C++11)
	class poisson_distribution;

	Produces  random non-negative integer values i, distributed according to
     discrete
	probability function:

	\(P(i | \mu) = \frac{e^{-\mu}\mu^i}{i!}\)P(i|I1/4) =

	e-I1/4
	A.I1/4i
	i!

	The value obtained is the probability of exactly i occurrences of a ran-
     dom event if
	the expected, mean number of its occurrence under  the	same  conditions
     (on the same
	time/space interval) is I1/4.

	std::poisson_distribution satisfies RandomNumberDistribution.

Template parameters
		  The  result type generated by the generator. The effect is un-
     defined if
	IntType - this is not one of  short,  int,  long,  long  long,	unsigned
     short, unsigned
		  int, unsigned long, or unsigned long long.

Member types
	Member type	    Definition
	result_type (C++11) IntType
	param_type  (C++11)  the type of the parameter set, see RandomNumberDis-
     tribution.

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
	mean	      returns the mean distribution parameter  (mean  number  of
     occurrences of
	(C++11)       the event)
		      (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 <iomanip>
      #include <iostream>
      #include <map>
      #include <random>
      #include <string>

      int main()
      {
	  std::random_device rd;
	  std::mt19937 gen(rd());

	  // If an event occurs 4 times a minute on average, how
	  // often is it that it occurs n times in one minute?
	  std::poisson_distribution<> d(4);

	  std::map<int, int> hist;
	  for (int n = 0; n != 10000; ++n)
	      ++hist[d(gen)];

	  for (auto [x, y] : hist)
	      std::cout << std::hex << x << ' '
			<< std::string(y / 100, '*') << '\n';
      }

Possible output:
      0 *
      1 *******
      2 **************
      3 *******************
      4 *******************
      5 ***************
      6 **********
      7 *****
      8 **
      9 *
      a
      b
      c
      d

External links
	  Weisstein, Eric W. "Poisson Distribution." From MathWorld a A  Wolfram
     Web
	  Resource.

http://cppreference.com 	   2024.06.10	    std::poisson_distribution(3)
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