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/* boost random/uniform_on_sphere.hpp header file
*
* Copyright Jens Maurer 2000-2001
* Copyright Steven Watanabe 2011
* 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 71018 2011-04-05 21:27:52Z steven_watanabe $
*
* 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/assert.hpp>
#include <boost/random/detail/config.hpp>
#include <boost/random/detail/operators.hpp>
#include <boost/random/normal_distribution.hpp>
namespace boost {
namespace random {
/**
* Instantiations of class template uniform_on_sphere model a
* \random_distribution. Such a distribution produces random
* numbers uniformly distributed on the unit sphere of arbitrary
* dimension @c dim. The @c Cont template parameter must be a STL-like
* container type with begin and end operations returning non-const
* ForwardIterators of type @c Cont::iterator.
*/
template<class RealType = double, class Cont = std::vector<RealType> >
class uniform_on_sphere
{
public:
typedef RealType input_type;
typedef Cont result_type;
class param_type
{
public:
typedef uniform_on_sphere distribution_type;
/**
* Constructs the parameters of a uniform_on_sphere
* distribution, given the dimension of the sphere.
*/
explicit param_type(int dim_arg = 2) : _dim(dim_arg)
{
BOOST_ASSERT(_dim >= 0);
}
/** Returns the dimension of the sphere. */
int dim() const { return _dim; }
/** Writes the parameters to a @c std::ostream. */
BOOST_RANDOM_DETAIL_OSTREAM_OPERATOR(os, param_type, parm)
{
os << parm._dim;
return os;
}
/** Reads the parameters from a @c std::istream. */
BOOST_RANDOM_DETAIL_ISTREAM_OPERATOR(is, param_type, parm)
{
is >> parm._dim;
return is;
}
/** Returns true if the two sets of parameters are equal. */
BOOST_RANDOM_DETAIL_EQUALITY_OPERATOR(param_type, lhs, rhs)
{ return lhs._dim == rhs._dim; }
/** Returns true if the two sets of parameters are different. */
BOOST_RANDOM_DETAIL_INEQUALITY_OPERATOR(param_type)
private:
int _dim;
};
/**
* Constructs a @c uniform_on_sphere distribution.
* @c dim is the dimension of the sphere.
*
* Requires: dim >= 0
*/
explicit uniform_on_sphere(int dim_arg = 2)
: _container(dim_arg), _dim(dim_arg) { }
/**
* Constructs a @c uniform_on_sphere distribution from its parameters.
*/
explicit uniform_on_sphere(const param_type& parm)
: _container(parm.dim()), _dim(parm.dim()) { }
// compiler-generated copy ctor and assignment operator are fine
/** Returns the dimension of the sphere. */
int dim() const { return _dim; }
/** Returns the parameters of the distribution. */
param_type param() const { return param_type(_dim); }
/** Sets the parameters of the distribution. */
void param(const param_type& parm)
{
_dim = parm.dim();
_container.resize(_dim);
}
/**
* Returns the smallest value that the distribution can produce.
* Note that this is required to approximate the standard library's
* requirements. The behavior is defined according to lexicographical
* comparison so that for a container type of std::vector,
* dist.min() <= x <= dist.max() where x is any value produced
* by the distribution.
*/
result_type min BOOST_PREVENT_MACRO_SUBSTITUTION () const
{
result_type result(_dim);
if(_dim != 0) {
result.front() = RealType(-1.0);
}
return result;
}
/**
* Returns the largest value that the distribution can produce.
* Note that this is required to approximate the standard library's
* requirements. The behavior is defined according to lexicographical
* comparison so that for a container type of std::vector,
* dist.min() <= x <= dist.max() where x is any value produced
* by the distribution.
*/
result_type max BOOST_PREVENT_MACRO_SUBSTITUTION () const
{
result_type result(_dim);
if(_dim != 0) {
result.front() = RealType(1.0);
}
return result;
}
/**
* Effects: Subsequent uses of the distribution do not depend
* on values produced by any engine prior to invoking reset.
*/
void reset() { _normal.reset(); }
/**
* Returns a point uniformly distributed over the surface of
* a sphere of dimension dim().
*/
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;
}
using std::sqrt;
// for all i: result[i] /= sqrt(sqsum)
std::transform(_container.begin(), _container.end(), _container.begin(),
std::bind2nd(std::divides<RealType>(), sqrt(sqsum)));
return _container;
}
/**
* Returns a point uniformly distributed over the surface of
* a sphere of dimension param.dim().
*/
template<class Engine>
result_type operator()(Engine& eng, const param_type& parm) const
{
return uniform_on_sphere(parm)(eng);
}
/** Writes the distribution to a @c std::ostream. */
BOOST_RANDOM_DETAIL_OSTREAM_OPERATOR(os, uniform_on_sphere, sd)
{
os << sd._dim;
return os;
}
/** Reads the distribution from a @c std::istream. */
BOOST_RANDOM_DETAIL_ISTREAM_OPERATOR(is, uniform_on_sphere, sd)
{
is >> sd._dim;
sd._container.resize(sd._dim);
return is;
}
/**
* Returns true if the two distributions will produce identical
* sequences of values, given equal generators.
*/
BOOST_RANDOM_DETAIL_EQUALITY_OPERATOR(uniform_on_sphere, lhs, rhs)
{ return lhs._dim == rhs._dim && lhs._normal == rhs._normal; }
/**
* Returns true if the two distributions may produce different
* sequences of values, given equal generators.
*/
BOOST_RANDOM_DETAIL_INEQUALITY_OPERATOR(uniform_on_sphere)
private:
normal_distribution<RealType> _normal;
result_type _container;
int _dim;
};
} // namespace random
using random::uniform_on_sphere;
} // namespace boost
#endif // BOOST_RANDOM_UNIFORM_ON_SPHERE_HPP
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