| Home | Libraries | People | FAQ | More

## Class template lagged_fibonacci_engine

boost::random::lagged_fibonacci_engine

## Synopsis

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

    template<typename UIntType, int w, unsigned int p, unsigned int q>
    class lagged_fibonacci_engine {
    public:
      // types
      typedef UIntType result_type;

      // construct/copy/destruct
      lagged_fibonacci_engine();
      explicit lagged_fibonacci_engine(UIntType);
      template<typename SeedSeq> explicit lagged_fibonacci_engine(SeedSeq &);
      template<typename It> lagged_fibonacci_engine(It &, It);

      // public static functions
      static result_type min();
      static result_type max();

      // public member functions
      void seed();
      void seed(UIntType);
      template<typename SeedSeq> void seed(SeedSeq &);
      template<typename It> void seed(It &, It);
      result_type operator()();
      template<typename Iter> void generate(Iter, Iter);
      void discard(boost::uintmax_t);

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

      // public data members
      static const bool has_fixed_range;
      static const int word_size;
      static const unsigned int long_lag;
      static const unsigned int short_lag;
      static const UIntType default_seed;
    };

## Description

Instantiations of class template lagged_fibonacci_engine model a pseudo-random number generator . It uses a lagged Fibonacci algorithm with two lags `p` and `q:` x(i) = x(i-p) + x(i-q) (mod 2w) with p > q.

### `lagged_fibonacci_engine` public construct/copy/destruct

1.     lagged_fibonacci_engine();

   Creates a new ``lagged_fibonacci_engine`` and calls `seed()`.

2.     explicit lagged_fibonacci_engine(UIntType value);

   Creates a new ``lagged_fibonacci_engine`` and calls `seed(value)`.

3.     template<typename SeedSeq> explicit lagged_fibonacci_engine(SeedSeq & seq);

   Creates a new ``lagged_fibonacci_engine`` and calls `seed(seq)`.

4.     template<typename It> lagged_fibonacci_engine(It & first, It last);

   Creates a new ``lagged_fibonacci_engine`` and calls `seed(first, last)`.

### `lagged_fibonacci_engine` public static functions

1.     static result_type min();

   Returns the smallest value that the generator can produce.

2.     static result_type max();

   Returns the largest value that the generator can produce.

### `lagged_fibonacci_engine` public member functions

1.     void seed();

   Calls `seed(default_seed)`.

2.     void seed(UIntType value);

   Sets the state of the generator to values produced by a `minstd_rand0` generator.

3.     template<typename SeedSeq> void seed(SeedSeq & seq);

   Sets the state of the generator using values produced by seq.

4.     template<typename It> void seed(It & first, It last);

   Sets the state of the generator to values from the iterator range [first, last). If there are not enough elements in the range [first, last) throws `std::invalid_argument`.

5.     result_type operator()();

   Returns the next value of the generator.

6.     template<typename Iter> void generate(Iter first, Iter last);

   Fills a range with random values

7.     void discard(boost::uintmax_t z);

   Advances the state of the generator by `z`.

### `lagged_fibonacci_engine` friend functions

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

   Writes the textual representation of the generator to a `std::ostream`.

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

   Reads the textual representation of the generator from a `std::istream`.

3.     friend bool operator==(const lagged_fibonacci_engine & x_,
                              const lagged_fibonacci_engine & y_);

   Returns true if the two generators will produce identical sequences of outputs.

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

   Returns true if the two generators will produce different sequences of outputs.