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boost/random/uniform_on_sphere.hpp

/* boost random/uniform_on_sphere.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: uniform_on_sphere.hpp 24096 2004-07-27 03:43:34Z dgregor $
 *
 * Revision history
 *  2001-02-18  moved to individual header files
 */

#ifndef BOOST_RANDOM_UNIFORM_ON_SPHERE_HPP
#define BOOST_RANDOM_UNIFORM_ON_SPHERE_HPP

#include <vector>
#include <algorithm>     // std::transform
#include <functional>    // std::bind2nd, std::divides
#include <boost/random/normal_distribution.hpp>

namespace boost {

template<class RealType = double, class Cont = std::vector<RealType> >
class uniform_on_sphere
{
public:
  typedef RealType input_type;
  typedef Cont result_type;

  explicit uniform_on_sphere(int dim = 2) : _container(dim), _dim(dim) { }

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

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

  template<class Engine>
  const result_type & operator()(Engine& eng)
  {
    RealType sqsum = 0;
    for(typename Cont::iterator it = _container.begin();
        it != _container.end();
        ++it) {
      RealType val = _normal(eng);
      *it = val;
      sqsum += val * val;
    }
#ifndef BOOST_NO_STDC_NAMESPACE
    using std::sqrt;
#endif
    // for all i: result[i] /= sqrt(sqsum)
    std::transform(_container.begin(), _container.end(), _container.begin(),
                   std::bind2nd(std::divides<RealType>(), sqrt(sqsum)));
    return _container;
  }

#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 uniform_on_sphere& sd)
  {
    os << sd._dim;
    return os;
  }

  template<class CharT, class Traits>
  friend std::basic_istream<CharT,Traits>&
  operator>>(std::basic_istream<CharT,Traits>& is, uniform_on_sphere& sd)
  {
    is >> std::ws >> sd._dim;
    sd._container.resize(sd._dim);
    return is;
  }
#endif

private:
  normal_distribution<RealType> _normal;
  result_type _container;
  int _dim;
};

} // namespace boost

#endif // BOOST_RANDOM_UNIFORM_ON_SPHERE_HPP