boost/random/triangle_distribution.hpp

   1 /* boost random/triangle_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_TRIANGLE_DISTRIBUTION_HPP
  17 #define BOOST_RANDOM_TRIANGLE_DISTRIBUTION_HPP
  18
  19 #include <boost/config/no_tr1/cmath.hpp>
  20 #include <cassert>
  21 #include <boost/random/detail/config.hpp>
  22 #include <boost/random/uniform_01.hpp>
  23
  24 namespace boost {
  25
  26 // triangle distribution, with a smallest, b most probable, and c largest
  27 // value.
  28 template<class RealType = double>
  29 class triangle_distribution
  30 {
  31 public:
  32   typedef RealType input_type;
  33   typedef RealType result_type;
  34
  35   explicit triangle_distribution(result_type a_arg = result_type(0),
  36                                  result_type b_arg = result_type(0.5),
  37                                  result_type c_arg = result_type(1))
  38     : _a(a_arg), _b(b_arg), _c(c_arg)
  39   {
  40     assert(_a <= _b && _b <= _c);
  41     init();
  42   }
  43
  44   // compiler-generated copy ctor and assignment operator are fine
  45   result_type a() const { return _a; }
  46   result_type b() const { return _b; }
  47   result_type c() const { return _c; }
  48
  49   void reset() { }
  50
  51   template<class Engine>
  52   result_type operator()(Engine& eng)
  53   {
  54 #ifndef BOOST_NO_STDC_NAMESPACE
  55     using std::sqrt;
  56 #endif
  57     result_type u = eng();
  58     if( u <= q1 )
  59       return _a + p1*sqrt(u);
  60     else
  61       return _c - d3*sqrt(d2*u-d1);
  62   }
  63
  64 #ifndef BOOST_RANDOM_NO_STREAM_OPERATORS
  65   template<class CharT, class Traits>
  66   friend std::basic_ostream<CharT,Traits>&
  67   operator<<(std::basic_ostream<CharT,Traits>& os, const triangle_distribution& td)
  68   {
  69     os << td._a << " " << td._b << " " << td._c;
  70     return os;
  71   }
  72
  73   template<class CharT, class Traits>
  74   friend std::basic_istream<CharT,Traits>&
  75   operator>>(std::basic_istream<CharT,Traits>& is, triangle_distribution& td)
  76   {
  77     is >> std::ws >> td._a >> std::ws >> td._b >> std::ws >> td._c;
  78     td.init();
  79     return is;
  80   }
  81 #endif
  82
  83 private:
  84   void init()
  85   {
  86 #ifndef BOOST_NO_STDC_NAMESPACE
  87     using std::sqrt;
  88 #endif
  89     d1 = _b - _a;
  90     d2 = _c - _a;
  91     d3 = sqrt(_c - _b);
  92     q1 = d1 / d2;
  93     p1 = sqrt(d1 * d2);
  94   }
  95
  96   result_type _a, _b, _c;
  97   result_type d1, d2, d3, q1, p1;
  98 };
  99
 100 } // namespace boost
 101
 102 #endif // BOOST_RANDOM_TRIANGLE_DISTRIBUTION_HPP