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]

26.6.8.4.2 Class template exponential_­distribution [rand.dist.pois.exp]

An exponential_­distribution random number distribution produces random numbers distributed according to the probability density function
template<class RealType = double>
  class exponential_distribution {
  public:
    // types
    using result_type = RealType;
    using param_type  = unspecified;

    // constructors and reset functions
    exponential_distribution() : exponential_distribution(1.0) {}
    explicit exponential_distribution(RealType lambda);
    explicit exponential_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
    RealType lambda() const;
    param_type param() const;
    void param(const param_type& parm);
    result_type min() const;
    result_type max() const;
  };
explicit exponential_distribution(RealType lambda);
Requires: .
Effects: Constructs an exponential_­distribution object; lambda corresponds to the parameter of the distribution.
RealType lambda() const;
Returns: The value of the lambda parameter with which the object was constructed.