boost/random/cauchy_distribution.hpp

   1 /* boost random/cauchy_distribution.hpp header file
   2  *
   3  * Copyright Jens Maurer 2000-2001
   4  * Distributed under the Boost Software License, Version 1.0. (See
   5  * accompanying file LICENSE_1_0.txt or copy at
   6  * http://www.boost.org/LICENSE_1_0.txt)
   7  *
   8  * See http://www.boost.org for most recent version including documentation.
   9  *
  10  * $Id$
  11  *
  12  * Revision history
  13  *  2001-02-18  moved to individual header files
  14  */
  15
  16 #ifndef BOOST_RANDOM_CAUCHY_DISTRIBUTION_HPP
  17 #define BOOST_RANDOM_CAUCHY_DISTRIBUTION_HPP
  18
  19 #include <boost/config/no_tr1/cmath.hpp>
  20 #include <iostream>
  21 #include <boost/limits.hpp>
  22 #include <boost/static_assert.hpp>
  23 #include <boost/random/detail/config.hpp>
  24
  25 namespace boost {
  26
  27 #if defined(__GNUC__) && (__GNUC__ < 3)
  28 // Special gcc workaround: gcc 2.95.x ignores using-declarations
  29 // in template classes (confirmed by gcc author Martin v. Loewis)
  30   using std::tan;
  31 #endif
  32
  33 // Cauchy distribution: p(x) = sigma/(pi*(sigma**2 + (x-median)**2))
  34 template<class RealType = double>
  35 class cauchy_distribution
  36 {
  37 public:
  38   typedef RealType input_type;
  39   typedef RealType result_type;
  40
  41 #ifndef BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS
  42   BOOST_STATIC_ASSERT(!std::numeric_limits<RealType>::is_integer);
  43 #endif
  44
  45   explicit cauchy_distribution(result_type median_arg = result_type(0),
  46                                result_type sigma_arg = result_type(1))
  47     : _median(median_arg), _sigma(sigma_arg) { }
  48
  49   // compiler-generated copy ctor and assignment operator are fine
  50
  51   result_type median() const { return _median; }
  52   result_type sigma() const { return _sigma; }
  53   void reset() { }
  54
  55   template<class Engine>
  56   result_type operator()(Engine& eng)
  57   {
  58     // Can we have a boost::mathconst please?
  59     const result_type pi = result_type(3.14159265358979323846);
  60 #ifndef BOOST_NO_STDC_NAMESPACE
  61     using std::tan;
  62 #endif
  63     return _median + _sigma * tan(pi*(eng()-result_type(0.5)));
  64   }
  65
  66 #ifndef BOOST_RANDOM_NO_STREAM_OPERATORS
  67   template<class CharT, class Traits>
  68   friend std::basic_ostream<CharT,Traits>&
  69   operator<<(std::basic_ostream<CharT,Traits>& os, const cauchy_distribution& cd)
  70   {
  71     os << cd._median << " " << cd._sigma;
  72     return os;
  73   }
  74
  75   template<class CharT, class Traits>
  76   friend std::basic_istream<CharT,Traits>&
  77   operator>>(std::basic_istream<CharT,Traits>& is, cauchy_distribution& cd)
  78   {
  79     is >> std::ws >> cd._median >> std::ws >> cd._sigma;
  80     return is;
  81   }
  82 #endif
  83
  84 private:
  85   result_type _median, _sigma;
  86 };
  87
  88 } // namespace boost
  89
  90 #endif // BOOST_RANDOM_CAUCHY_DISTRIBUTION_HPP