/* boost random/lognormal_distribution.hpp header file

  *

  * Copyright Jens Maurer 2000-2001

  * Distributed under the Boost Software License, Version 1.0. (See

  * accompanying file LICENSE_1_0.txt or copy at

  * http://www.boost.org/LICENSE_1_0.txt)

  *

  * See http://www.boost.org for most recent version including documentation.

  *

  * $Id: lognormal_distribution.hpp,v 1.16 2004/07/27 03:43:32 dgregor Exp $

  *

  * Revision history

  *  2001-02-18  moved to individual header files

  */

 #ifndef BOOST_RANDOM_LOGNORMAL_DISTRIBUTION_HPP

 #define BOOST_RANDOM_LOGNORMAL_DISTRIBUTION_HPP

 #include <cmath>      // std::exp, std::sqrt

 #include <cassert>

 #include <iostream>

 #include <boost/limits.hpp>

 #include <boost/static_assert.hpp>

 #include <boost/random/normal_distribution.hpp>

 #ifdef BOOST_NO_STDC_NAMESPACE

 namespace std {

   using ::log;

   using ::sqrt;

 }

 #endif

 namespace boost {

 #if defined(__GNUC__) && (__GNUC__ < 3)

 // Special gcc workaround: gcc 2.95.x ignores using-declarations

 // in template classes (confirmed by gcc author Martin v. Loewis)

   using std::sqrt;

   using std::exp;

 #endif

 template<class RealType = double>

 class lognormal_distribution

 {

 public:

   typedef typename normal_distribution<RealType>::input_type input_type;

   typedef RealType result_type;

 #ifndef BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS

     BOOST_STATIC_ASSERT(!std::numeric_limits<RealType>::is_integer);

 #endif

   explicit lognormal_distribution(result_type mean = result_type(1),

                                   result_type sigma = result_type(1))

     : _mean(mean), _sigma(sigma)

   { 

     assert(mean > result_type(0));

     init();

   }

   // compiler-generated copy ctor and assignment operator are fine

   RealType& mean() const { return _mean; }

   RealType& sigma() const { return _sigma; }

   void reset() { _normal.reset(); }

   template<class Engine>

   result_type operator()(Engine& eng)

   {

 #ifndef BOOST_NO_STDC_NAMESPACE

     // allow for Koenig lookup

     using std::exp;

 #endif

     return exp(_normal(eng) * _nsigma + _nmean);

   }

 #if !defined(BOOST_NO_OPERATORS_IN_NAMESPACE) && !defined(BOOST_NO_MEMBER_TEMPLATE_FRIENDS)

   template<class CharT, class Traits>

   friend std::basic_ostream<CharT,Traits>&

   operator<<(std::basic_ostream<CharT,Traits>& os, const lognormal_distribution& ld)

   {

     os << ld._normal << " " << ld._mean << " " << ld._sigma;

     return os;

   }

   template<class CharT, class Traits>

   friend std::basic_istream<CharT,Traits>&

   operator>>(std::basic_istream<CharT,Traits>& is, lognormal_distribution& ld)

   {

     is >> std::ws >> ld._normal >> std::ws >> ld._mean >> std::ws >> ld._sigma;

     ld.init();

     return is;

   }

 #endif

 private:

   void init()

   {

 #ifndef BOOST_NO_STDC_NAMESPACE

     // allow for Koenig lookup

     using std::exp; using std::log; using std::sqrt;

 #endif

     _nmean = log(_mean*_mean/sqrt(_sigma*_sigma + _mean*_mean));

     _nsigma = sqrt(log(_sigma*_sigma/_mean/_mean+result_type(1)));

   }

   RealType _mean, _sigma;

   RealType _nmean, _nsigma;

   normal_distribution<result_type> _normal;

 };

 } // namespace boost

 #endif // BOOST_RANDOM_LOGNORMAL_DISTRIBUTION_HPP