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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|) =

		  e-
		  i
		  i!

	  The  value obtained is the probability of exactly i occurrences of a
       random event if
	  the expected,	mean number of its occurrence under  the  same	condi-
       tions (on the same
	  time/space interval) is .

	  std::poisson_distribution satisfies RandomNumberDistribution

Template parameters
		    The	 result	type generated by the generator. The effect is
       undefined 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	    IntType
	  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
			returns	the mean distribution parameter	 (mean	number
       of occurrences of
	  mean		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 <iostream>
	#include <iomanip>
	#include <string>
	#include <map>
	#include <random>
	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 p : hist) {
		std::cout << std::hex << p.first << ' '
			  << std::string(p.second/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 Wolfram
       Web Resource.

http://cppreference.com		  2022.07.31	  std::poisson_distribution(3)

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