williamr@2: /* boost random/uniform_on_sphere.hpp header file
williamr@2:  *
williamr@2:  * Copyright Jens Maurer 2000-2001
williamr@2:  * Distributed under the Boost Software License, Version 1.0. (See
williamr@2:  * accompanying file LICENSE_1_0.txt or copy at
williamr@2:  * http://www.boost.org/LICENSE_1_0.txt)
williamr@2:  *
williamr@2:  * See http://www.boost.org for most recent version including documentation.
williamr@2:  *
williamr@2:  * $Id: uniform_on_sphere.hpp,v 1.11 2004/07/27 03:43:32 dgregor Exp $
williamr@2:  *
williamr@2:  * Revision history
williamr@2:  *  2001-02-18  moved to individual header files
williamr@2:  */
williamr@2: 
williamr@2: #ifndef BOOST_RANDOM_UNIFORM_ON_SPHERE_HPP
williamr@2: #define BOOST_RANDOM_UNIFORM_ON_SPHERE_HPP
williamr@2: 
williamr@2: #include <vector>
williamr@2: #include <algorithm>     // std::transform
williamr@2: #include <functional>    // std::bind2nd, std::divides
williamr@2: #include <boost/random/normal_distribution.hpp>
williamr@2: 
williamr@2: namespace boost {
williamr@2: 
williamr@2: template<class RealType = double, class Cont = std::vector<RealType> >
williamr@2: class uniform_on_sphere
williamr@2: {
williamr@2: public:
williamr@2:   typedef RealType input_type;
williamr@2:   typedef Cont result_type;
williamr@2: 
williamr@2:   explicit uniform_on_sphere(int dim = 2) : _container(dim), _dim(dim) { }
williamr@2: 
williamr@2:   // compiler-generated copy ctor and assignment operator are fine
williamr@2: 
williamr@2:   void reset() { _normal.reset(); }
williamr@2: 
williamr@2:   template<class Engine>
williamr@2:   const result_type & operator()(Engine& eng)
williamr@2:   {
williamr@2:     RealType sqsum = 0;
williamr@2:     for(typename Cont::iterator it = _container.begin();
williamr@2:         it != _container.end();
williamr@2:         ++it) {
williamr@2:       RealType val = _normal(eng);
williamr@2:       *it = val;
williamr@2:       sqsum += val * val;
williamr@2:     }
williamr@2: #ifndef BOOST_NO_STDC_NAMESPACE
williamr@2:     using std::sqrt;
williamr@2: #endif
williamr@2:     // for all i: result[i] /= sqrt(sqsum)
williamr@2:     std::transform(_container.begin(), _container.end(), _container.begin(),
williamr@2:                    std::bind2nd(std::divides<RealType>(), sqrt(sqsum)));
williamr@2:     return _container;
williamr@2:   }
williamr@2: 
williamr@2: #if !defined(BOOST_NO_OPERATORS_IN_NAMESPACE) && !defined(BOOST_NO_MEMBER_TEMPLATE_FRIENDS)
williamr@2:   template<class CharT, class Traits>
williamr@2:   friend std::basic_ostream<CharT,Traits>&
williamr@2:   operator<<(std::basic_ostream<CharT,Traits>& os, const uniform_on_sphere& sd)
williamr@2:   {
williamr@2:     os << sd._dim;
williamr@2:     return os;
williamr@2:   }
williamr@2: 
williamr@2:   template<class CharT, class Traits>
williamr@2:   friend std::basic_istream<CharT,Traits>&
williamr@2:   operator>>(std::basic_istream<CharT,Traits>& is, uniform_on_sphere& sd)
williamr@2:   {
williamr@2:     is >> std::ws >> sd._dim;
williamr@2:     sd._container.resize(sd._dim);
williamr@2:     return is;
williamr@2:   }
williamr@2: #endif
williamr@2: 
williamr@2: private:
williamr@2:   normal_distribution<RealType> _normal;
williamr@2:   result_type _container;
williamr@2:   int _dim;
williamr@2: };
williamr@2: 
williamr@2: } // namespace boost
williamr@2: 
williamr@2: #endif // BOOST_RANDOM_UNIFORM_ON_SPHERE_HPP