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## Class template gamma_distribution

boost::random::gamma_distribution

## Synopsis

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

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

      // member classes/structs/unions

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

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

        // public member functions
        RealType alpha() const;
        RealType beta() 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 > &, param_type &);
        friend bool operator==(const param_type &, const param_type &);
        friend bool operator!=(const param_type &, const param_type &);
      };

      // construct/copy/destruct
      explicit gamma_distribution(const result_type & = 1.0,
                                  const result_type & = 1.0);
      explicit gamma_distribution(const param_type &);

      // public member functions
      RealType alpha() const;
      RealType beta() 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 &);
      template<typename URNG>
        RealType operator()(URNG &, const param_type &) const;

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

## Description

The gamma distribution is a continuous distribution with two parameters alpha and beta. It produces values > 0.

It has .

### `gamma_distribution` public construct/copy/destruct

1.     explicit gamma_distribution(const result_type & alpha = 1.0,
                                   const result_type & beta = 1.0);

   Creates a new `gamma_distribution` with parameters "alpha" and "beta".

   Requires: alpha > 0 && beta > 0

2.     explicit gamma_distribution(const param_type & param);

   Constructs a ``gamma_distribution`` from its parameters.

### `gamma_distribution` public member functions

1.     RealType alpha() const;

   Returns the "alpha" paramter of the distribution.

2.     RealType beta() const;

   Returns the "beta" parameter of the distribution.

3.     RealType min() const;

   Returns the smallest value that the distribution can produce.

4.     RealType max() const;

5.     param_type param() const;

   Returns the parameters of the distribution.

6.     void param(const param_type & param);

   Sets the parameters of the distribution.

7.     void reset();

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

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

   Returns a random variate distributed according to the gamma distribution.

9.     template<typename URNG>
         RealType operator()(URNG & urng, const param_type & param) const;

### `gamma_distribution` friend functions

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

   Writes a ``gamma_distribution`` to a `std::ostream`.

2.     template<typename CharT, typename Traits>
         friend std::basic_istream< CharT, Traits > &
         operator>>(std::basic_istream< CharT, Traits > & is,
                    gamma_distribution & gd);

   Reads a ``gamma_distribution`` from a `std::istream`.

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

   Returns true if the two distributions will produce identical sequences of random variates given equal generators.

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

   Returns true if the two distributions can produce different sequences of random variates, given equal generators.