26 Numerics library [numerics]

26.6 Random number generation [rand]

26.6.8 Random number distribution class templates [rand.dist]

26.6.8.4 Poisson distributions [rand.dist.pois]

26.6.8.4.1 Class template poisson_distribution [rand.dist.pois.poisson]

1

A poisson_distribution random number distribution produces integer values i ≥ 0 distributed according to the discrete probability function \[% P(i\,|\,\mu) = \frac{ e^{-\mu} \mu^{i} } { i\,! } \; \mbox{.} \] The distribution parameter μ is also known as this distribution's mean.

template<class IntType = int>
 class poisson_distribution{
public:
 // 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);

2

Requires: 0 < mean .

3

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

double mean() const;

4

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