Class template discrete_distribution

boost::random::discrete_distribution

Synopsis

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

template<typename IntType = int, typename WeightType = double> 
class discrete_distribution {
public:
  // types
  typedef WeightType input_type; 
  typedef IntType    result_type;

  // member classes/structs/unions

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

    // public member functions
    param_type();
    template<typename Iter> param_type(Iter, Iter);
    param_type(const std::initializer_list< WeightType > &);
    template<typename Range> explicit param_type(const Range &);
    template<typename Func> param_type(std::size_t, double, double, Func);
    std::vector< WeightType > probabilities() 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 > &, const param_type &);
    bool operator==(const param_type &, const param_type &);
    bool operator!=(const param_type &, const param_type &);
  };

  // public member functions
  discrete_distribution();
  template<typename Iter> discrete_distribution(Iter, Iter);
  discrete_distribution(std::initializer_list< WeightType >);
  template<typename Range> explicit discrete_distribution(const Range &);
  template<typename Func> 
    discrete_distribution(std::size_t, double, double, Func);
  explicit discrete_distribution(const param_type &);
  template<typename URNG> IntType operator()(URNG &) const;
  template<typename URNG> IntType operator()(URNG &, const param_type &) const;
  result_type min() const;
  result_type max() const;
  std::vector< WeightType > probabilities() 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 discrete_distribution &);
  template<typename CharT, typename Traits> 
    std::basic_istream< CharT, Traits > & 
    operator>>(std::basic_istream< CharT, Traits > &, 
               const discrete_distribution &);
  bool operator==(const discrete_distribution &, 
                  const discrete_distribution &);
  bool operator!=(const discrete_distribution &, 
                  const discrete_distribution &);
};

Description

The class discrete_distribution models a random distribution . It produces integers in the range [0, n) with the probability of producing each value is specified by the parameters of the distribution.

`discrete_distribution` public member functions

```
discrete_distribution();
```
Creates a new discrete_distribution object that has and .
```
template<typename Iter> discrete_distribution(Iter first, Iter last);
```
Constructs a discrete_distribution from an iterator range. If first == last, equivalent to the default constructor. Otherwise, the values of the range represent weights for the possible values of the distribution.
```
discrete_distribution(std::initializer_list< WeightType > wl);
```
Constructs a discrete_distribution from a std::initializer_list. If the initializer_list is empty, equivalent to the default constructor. Otherwise, the values of the initializer_list represent weights for the possible values of the distribution. For example, given the distribution
```
discrete_distribution<> dist{1, 4, 5};
```
The probability of a 0 is 1/10, the probability of a 1 is 2/5, the probability of a 2 is 1/2, and no other values are possible.
```
template<typename Range> explicit discrete_distribution(const Range & range);
```
Constructs a discrete_distribution from a Boost.Range range. If the range is empty, equivalent to the default constructor. Otherwise, the values of the range represent weights for the possible values of the distribution.
```
template<typename Func> 
  discrete_distribution(std::size_t nw, double xmin, double xmax, Func fw);
```
Constructs a discrete_distribution that approximates a function. If nw is zero, equivalent to the default constructor. Otherwise, the range of the distribution is [0, nw), and the weights are found by calling fw with values evenly distributed between and , where .

explicit discrete_distribution(const param_type & param);

Constructs a discrete_distribution from its parameters.

```
template<typename URNG> IntType operator()(URNG & urng) const;
```
Returns a value distributed according to the parameters of the discrete_distribution.

template<typename URNG> 
  IntType operator()(URNG & urng, const param_type & param) const;

Returns a value distributed according to the parameters specified by param.

```
result_type min() const;
```
Returns the smallest value that the distribution can produce.
```
result_type max() const;
```
Returns the largest value that the distribution can produce.
```
std::vector< WeightType > probabilities() const;
```
Returns a vector containing the probabilities of each value of the distribution. For example, given
```
discrete_distribution<> dist = { 1, 4, 5 };
std::vector<double> p = dist.param();
```
the vector, p will contain {0.1, 0.4, 0.5}.

If WeightType is integral, then the weights will be returned unchanged.
```
param_type param() const;
```
Returns the parameters of the distribution.
```
void param(const param_type & param);
```
Sets the parameters of the distribution.
```
void reset();
```
Effects: Subsequent uses of the distribution do not depend on values produced by any engine prior to invoking reset.

`discrete_distribution` friend functions

template<typename CharT, typename Traits> 
  std::basic_ostream< CharT, Traits > & 
  operator<<(std::basic_ostream< CharT, Traits > & os, 
             const discrete_distribution & dd);

Writes a distribution to a std::ostream.

template<typename CharT, typename Traits> 
  std::basic_istream< CharT, Traits > & 
  operator>>(std::basic_istream< CharT, Traits > & is, 
             const discrete_distribution & dd);

Reads a distribution from a std::istream

bool operator==(const discrete_distribution & lhs, 
                const discrete_distribution & rhs);

Returns true if the two distributions will return the same sequence of values, when passed equal generators.

bool operator!=(const discrete_distribution & lhs, 
                const discrete_distribution & rhs);

Returns true if the two distributions may return different sequences of values, when passed equal generators.

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