boost/random/uniform_on_sphere.hpp

   1 /* boost random/uniform_on_sphere.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_UNIFORM_ON_SPHERE_HPP
  17 #define BOOST_RANDOM_UNIFORM_ON_SPHERE_HPP
  18
  19 #include <vector>
  20 #include <algorithm>     // std::transform
  21 #include <functional>    // std::bind2nd, std::divides
  22 #include <boost/random/detail/config.hpp>
  23 #include <boost/random/normal_distribution.hpp>
  24
  25 namespace boost {
  26
  27 template<class RealType = double, class Cont = std::vector<RealType> >
  28 class uniform_on_sphere
  29 {
  30 public:
  31   typedef RealType input_type;
  32   typedef Cont result_type;
  33
  34   explicit uniform_on_sphere(int dim = 2) : _container(dim), _dim(dim) { }
  35
  36   // compiler-generated copy ctor and assignment operator are fine
  37
  38   void reset() { _normal.reset(); }
  39
  40   template<class Engine>
  41   const result_type & operator()(Engine& eng)
  42   {
  43     RealType sqsum = 0;
  44     for(typename Cont::iterator it = _container.begin();
  45         it != _container.end();
  46         ++it) {
  47       RealType val = _normal(eng);
  48       *it = val;
  49       sqsum += val * val;
  50     }
  51 #ifndef BOOST_NO_STDC_NAMESPACE
  52     using std::sqrt;
  53 #endif
  54     // for all i: result[i] /= sqrt(sqsum)
  55     std::transform(_container.begin(), _container.end(), _container.begin(),
  56                    std::bind2nd(std::divides<RealType>(), sqrt(sqsum)));
  57     return _container;
  58   }
  59
  60 #ifndef BOOST_RANDOM_NO_STREAM_OPERATORS
  61   template<class CharT, class Traits>
  62   friend std::basic_ostream<CharT,Traits>&
  63   operator<<(std::basic_ostream<CharT,Traits>& os, const uniform_on_sphere& sd)
  64   {
  65     os << sd._dim;
  66     return os;
  67   }
  68
  69   template<class CharT, class Traits>
  70   friend std::basic_istream<CharT,Traits>&
  71   operator>>(std::basic_istream<CharT,Traits>& is, uniform_on_sphere& sd)
  72   {
  73     is >> std::ws >> sd._dim;
  74     sd._container.resize(sd._dim);
  75     return is;
  76   }
  77 #endif
  78
  79 private:
  80   normal_distribution<RealType> _normal;
  81   result_type _container;
  82   int _dim;
  83 };
  84
  85 } // namespace boost
  86
  87 #endif // BOOST_RANDOM_UNIFORM_ON_SPHERE_HPP