C++

Reference

<random>

poisson_distribution

class template
<random>

std::poisson_distribution

template <class IntType = int> class poisson_distribution;
Poisson distribution
Random number distribution that produces integers according to a Poisson distribution, which is described by the following probability mass function:



This distribution produces random integers where each value represents a specific count of independent events occurring within a fixed interval, based on the observed mean rate at which they appear to happen (μ).

The distribution parameter, mean (μ), is set on construction.

To produce a random value following this distribution, call its member function operator().

Template parameters

IntType
An integer type. Aliased as member type result_type.
By default, this is int.

Member types

The following aliases are member types of poisson_distribution:

member typedefinitionnotes
result_typeThe first template parameter (IntType)The type of the numbers generated (defaults to int)
param_typenot specifiedThe type returned by member param.

Member functions

(constructor)
Construct Poisson distribution (public member function)
operator()
Generate random number (public member function)
reset
Reset distribution (public member function)
param
Distribution parameters (public member function)
min
Minimum value (public member function)
max
Maximum value (public member function)

Distribution parameters

mean
Mean (public member function)

Non-member functions

operator<<
Insert into output stream (function template)
operator>>
Extract from input stream (function template)
relational operators
Relational operators (function template)

Example

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// poisson_distribution
#include <iostream>
#include <random>

int main()
{
  const int nrolls = 10000; // number of experiments
  const int nstars = 100;   // maximum number of stars to distribute

  std::default_random_engine generator;
  std::poisson_distribution<int> distribution(4.1);

  int p[10]={};

  for (int i=0; i<nrolls; ++i) {
    int number = distribution(generator);
    if (number<10) ++p[number];
  }

  std::cout << "poisson_distribution (mean=4.1):" << std::endl;
  for (int i=0; i<10; ++i)
    std::cout << i << ": " << std::string(p[i]*nstars/nrolls,'*') << std::endl;

  return 0;
}

Possible output:

poisson_distribution (mean=4.1):
0: *
1: ******
2: *************
3: *******************
4: *******************
5: ***************
6: ***********
7: ******
8: ***
9: *


See also

uniform_int_distribution
Uniform discrete distribution (class template)
exponential_distribution
Exponential distribution (class template)
gamma_distribution
Gamma distribution (class template)