std::poisson_distribution

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-μ·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.

Member types

Template:tdcl list hitemTemplate:tdcl list itemTemplate:tdcl list item

Member functions

Template:cpp/numeric/random/distribution/dcl list constructorTemplate:cpp/numeric/random/distribution/dcl list resetTemplate:cpp/numeric/random/distribution/dcl list operator()Template:cpp/numeric/random/poisson distribution/dcl list meanTemplate:cpp/numeric/random/distribution/dcl list paramTemplate:cpp/numeric/random/distribution/dcl list minTemplate:cpp/numeric/random/distribution/dcl list max

Generation

Characteristics

Non-member functions

Template:cpp/numeric/random/distribution/dcl list operator cmpTemplate:cpp/numeric/random/distribution/dcl list operator ltltgtgt

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

Output:

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

External links

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