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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