+
+ /**
+ * @brief A normal continuous distribution for random numbers.
+ *
+ * The formula for the normal probability mass function is
+ * @f$ p(x) = \frac{1}{\sigma \sqrt{2 \pi}}
+ * e^{- \frac{{x - mean}^ {2}}{2 \sigma ^ {2}} } @f$.
+ */
+ template<typename _RealType = double>
+ class normal_distribution
+ {
+ public:
+ // types
+ typedef _RealType input_type;
+ typedef _RealType result_type;
+
+ public:
+ /**
+ * Constructs a normal distribution with parameters @f$ mean @f$ and
+ * @f$ \sigma @f$.
+ */
+ explicit
+ normal_distribution(const result_type& __mean = result_type(0),
+ const result_type& __sigma = result_type(1))
+ : _M_mean(__mean), _M_sigma(__sigma), _M_saved_available(false)
+ {
+ _GLIBCXX_DEBUG_ASSERT(_M_sigma > 0);
+ }
+
+ /**
+ * Gets the mean of the distribution.
+ */
+ _RealType
+ mean() const
+ { return _M_mean; }
+
+ /**
+ * Gets the @f$ \sigma @f$ of the distribution.
+ */
+ _RealType
+ sigma() const
+ { return _M_sigma; }
+
+ /**
+ * Resets the distribution.
+ */
+ void
+ reset()
+ { _M_saved_available = false; }
+
+ template<class _UniformRandomNumberGenerator>
+ result_type
+ operator()(_UniformRandomNumberGenerator& __urng);
+
+ /**
+ * Inserts a %normal_distribution random number distribution
+ * @p __x into the output stream @p __os.
+ *
+ * @param __os An output stream.
+ * @param __x A %normal_distribution random number distribution.
+ *
+ * @returns The output stream with the state of @p __x inserted or in
+ * an error state.
+ */
+ template<typename _CharT, typename _Traits>
+ friend std::basic_ostream<_CharT, _Traits>&
+ operator<<(std::basic_ostream<_CharT, _Traits>& __os,
+ const normal_distribution& __x)
+ {
+ return __os << __x.mean() << " " << __x.sigma()
+ << " " << __x._M_saved << " " << __x._M_saved_available;
+ }
+
+ /**
+ * Extracts a %normal_distribution random number distribution
+ * @p __u from the input stream @p __is.
+ *
+ * @param __is An input stream.
+ * @param __u A %normal_distribution random number generator engine.
+ *
+ * @returns The input stream with @p __u extracted or in an error state.
+ */
+ template<typename _CharT, typename _Traits>
+ friend std::basic_istream<_CharT, _Traits>&
+ operator>>(std::basic_istream<_CharT, _Traits>& __is,
+ normal_distribution& __u)
+ {
+ return __is >> __u._M_mean >> __u._M_sigma
+ >> __u._M_saved >> __u._M_saved_available;
+ }
+
+ private:
+ result_type _M_mean;
+ result_type _M_sigma;
+ result_type _M_saved;
+ bool _M_saved_available;
+ };
+