| Home | Libraries | People | FAQ | More

## Class template chi_squared_distribution

boost::random::chi_squared_distribution

## Synopsis

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

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

      // member classes/structs/unions

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

        // public member functions
        explicit param_type(RealType = 1);
        RealType n() const;

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

      // public member functions
      explicit chi_squared_distribution(RealType = 1);
      explicit chi_squared_distribution(const param_type &);
      template<typename URNG> RealType operator()(URNG &);
      template<typename URNG>
        RealType operator()(URNG &, const param_type &) const;
      RealType n() const;
      RealType min() const;
      RealType max() const;
      param_type param() const;
      void param(const param_type &);
      void reset();

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

## Description

The chi squared distribution is a real valued distribution with one parameter, `n`. The distribution produces values > 0.

The distribution function is .

### `chi_squared_distribution` public member functions

1.     explicit chi_squared_distribution(RealType n = 1);

   Construct a `chi_squared_distribution` object. `n` is the parameter of the distribution.

   Requires: t >=0 && 0 <= p <= 1

2.     explicit chi_squared_distribution(const param_type & param);

   Construct an `chi_squared_distribution` object from the parameters.

3.     template<typename URNG> RealType operator()(URNG & urng);

   Returns a random variate distributed according to the chi squared distribution.

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

   Returns a random variate distributed according to the chi squared distribution with parameters specified by `param`.

5.     RealType n() const;

   Returns the `n` parameter of the distribution.

6.     RealType min() const;

   Returns the smallest value that the distribution can produce.

7.     RealType max() const;

   Returns the largest value that the distribution can produce.

8.     param_type param() const;

   Returns the parameters of the distribution.

9.     void param(const param_type & param);

   Sets parameters of the distribution.

10.     void reset();

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

### `chi_squared_distribution` friend functions

1.     template<typename CharT, typename Traits>
         std::basic_ostream< CharT, Traits > &
         operator<<(std::basic_ostream< CharT, Traits > & os,
                    const chi_squared_distribution & c2d);

   Writes the parameters of the distribution to a `std::ostream`.

2.     template<typename CharT, typename Traits>
         std::basic_istream< CharT, Traits > &
         operator>>(std::basic_istream< CharT, Traits > & is,
                    chi_squared_distribution & c2d);

   Reads the parameters of the distribution from a `std::istream`.

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

   Returns true if the two distributions will produce the same sequence of values, given equal generators.

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

   Returns true if the two distributions could produce different sequences of values, given equal generators.