29 Numerics library [numerics]

29.6 Random number generation [rand]

29.6.8 Random number distribution class templates [rand.dist] Poisson distributions [rand.dist.pois] Class template poisson_­distribution [rand.dist.pois.poisson]

A poisson_­distribution random number distribution produces integer values i0 distributed according to the discrete probability function


The distribution parameter μ is also known as this distribution's mean.

template<class IntType = int>
  class poisson_distribution
    // types
    using result_type = IntType;
    using param_type  = unspecified;

    // constructors and reset functions
    explicit poisson_distribution(double mean = 1.0);
    explicit poisson_distribution(const param_type& parm);
    void reset();

    // generating functions
    template<class URBG>
      result_type operator()(URBG& g);
    template<class URBG>
      result_type operator()(URBG& g, const param_type& parm);

    // property functions
    double mean() const;
    param_type param() const;
    void param(const param_type& parm);
    result_type min() const;
    result_type max() const;

explicit poisson_distribution(double mean = 1.0);

Requires: 0<mean.

Effects: Constructs a poisson_­distribution object; mean corresponds to the parameter of the distribution.

double mean() const;

Returns: The value of the mean parameter with which the object was constructed.