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## Class template exponential_distribution

boost::random::exponential_distribution

## Synopsis

    // In header: <boost/random/exponential_distribution.hpp>

    template<typename RealType = double>
    class exponential_distribution {
    public:
      // types
      typedef RealType input_type;
      typedef RealType result_type;

      // member classes/structs/unions

      class param_type {
      public:
        // types
        typedef exponential_distribution distribution_type;

        // construct/copy/destruct
        param_type(RealType = 1.0);

        // public member functions
        RealType lambda() const;

        // friend functions
        template<typename CharT, typename Traits>
          friend std::basic_ostream< CharT, Traits > &
          operator<<(std::basic_ostream< CharT, Traits > &, const param_type &);
        template<typename CharT, typename Traits>
          friend std::basic_istream< CharT, Traits > &
          operator>>(std::basic_istream< CharT, Traits > &, const param_type &);
        friend bool operator==(const param_type &, const param_type &);
        friend bool operator!=(const param_type &, const param_type &);
      };

      // construct/copy/destruct
      explicit exponential_distribution(RealType = 1.0);
      explicit exponential_distribution(const param_type &);

      // public member functions
      RealType lambda() const;
      RealType min() const;
      RealType max() const;
      param_type param() const;
      void param(const param_type &);
      void reset();
      template<typename Engine> result_type operator()(Engine &) const;
      template<typename Engine>
        result_type operator()(Engine &, const param_type &) const;

      // friend functions
      template<typename CharT, typename Traits>
        friend std::basic_ostream< CharT, Traits > &
        operator<<(std::basic_ostream< CharT, Traits > &,
                   const exponential_distribution &);
      template<typename CharT, typename Traits>
        friend std::basic_istream< CharT, Traits > &
        operator>>(std::basic_istream< CharT, Traits > &,
                   const exponential_distribution &);
      friend bool operator==(const exponential_distribution &,
                             const exponential_distribution &);
      friend bool operator!=(const exponential_distribution &,
                             const exponential_distribution &);
    };

## Description

The exponential distribution is a model of random distribution with a single parameter lambda.

It has

The implementation uses the "ziggurat" algorithm, as described in

> "The Ziggurat Method for Generating Random Variables", George Marsaglia and Wai Wan Tsang, Journal of Statistical Software Volume 5, Number 8 (2000), 1-7.

### `exponential_distribution` public construct/copy/destruct

1.     explicit exponential_distribution(RealType lambda = 1.0);

   Constructs an `exponential_distribution` with a given lambda.

   Requires: lambda > 0

2.     explicit exponential_distribution(const param_type & param);

   Constructs an `exponential_distribution` from its parameters

### `exponential_distribution` public member functions

1.     RealType lambda() const;

   Returns the lambda parameter of the distribution.

2.     RealType min() const;

   Returns the smallest value that the distribution can produce.

3.     RealType max() const;

   Returns the largest value that the distribution can produce.

4.     param_type param() const;

   Returns the parameters of the distribution.

5.     void param(const param_type & param);

   Sets the parameters of the distribution.

6.     void reset();

   Effects: Subsequent uses of the distribution do not depend on values produced by any engine prior to invoking reset.

7.     template<typename Engine> result_type operator()(Engine & eng) const;

   Returns a random variate distributed according to the exponential distribution.

8.     template<typename Engine>
         result_type operator()(Engine & eng, const param_type & param) const;

   Returns a random variate distributed according to the exponential distribution with parameters specified by param.

### `exponential_distribution` friend functions

1.     template<typename CharT, typename Traits>
         friend std::basic_ostream< CharT, Traits > &
         operator<<(std::basic_ostream< CharT, Traits > & os,
                    const exponential_distribution & ed);

   Writes the distribution to a std::ostream.

2.     template<typename CharT, typename Traits>
         friend std::basic_istream< CharT, Traits > &
         operator>>(std::basic_istream< CharT, Traits > & is,
                    const exponential_distribution & ed);

   Reads the distribution from a std::istream.

3.     friend bool operator==(const exponential_distribution & lhs,
                              const exponential_distribution & rhs);

   Returns true iff the two distributions will produce identical sequences of values given equal generators.

4.     friend bool operator!=(const exponential_distribution & lhs,
                              const exponential_distribution & rhs);

   Returns true iff the two distributions will produce different sequences of values given equal generators.