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std::poisson_distribution

From cppreference.com
< cpp‎ | numeric‎ | random
 
 
 
 
 
Defined in header <random>
template< class IntType = int >
class poisson_distribution;
(since C++11)

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

P(i|μ) =
e
·μi
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 conditions (on the same time/space interval) is μ.

Contents

[edit] Member types

Member type Definition
result_type IntType
param_type the type of the parameter set, unspecified

[edit] Member functions

constructs new distribution
(public member function) [edit]
resets the internal state of the distribution
(public member function) [edit]
Generation
generates the next random number in the distribution
(public member function) [edit]
Characteristics
returns the mean distribution parameter (mean number of occurrences of the event)
(public member function) [edit]
gets or sets the distribution parameter object
(public member function) [edit]
returns the minimum potentially generated value
(public member function) [edit]
returns the maximum potentially generated value
(public member function) [edit]

[edit] Non-member functions

compares two distribution objects
(function) [edit]
performs stream input and output on pseudo-random number distribution
(function) [edit]

[edit] Example

#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 << p.first <<
                ' ' << std::string(p.second/100, '*') << '\n';
    }
}

Output:

0 *
1 *******
2 **************
3 *******************
4 *******************
5 ***************
6 **********
7 *****
8 **
9 *
10 
11 
12 
13

[edit] External links

Weisstein, Eric W. "Poisson Distribution." From MathWorld--A Wolfram Web Resource.