/* 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,v 1.11 2004/07/27 03:43:32 dgregor Exp $

 *

 * 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