--- /dev/null
+/* boost random/piecewise_constant_distribution.hpp header file
+ *
+ * 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: piecewise_constant_distribution.hpp 85813 2013-09-21 20:17:00Z jewillco $
+ */
+
+#ifndef BOOST_RANDOM_PIECEWISE_CONSTANT_DISTRIBUTION_HPP_INCLUDED
+#define BOOST_RANDOM_PIECEWISE_CONSTANT_DISTRIBUTION_HPP_INCLUDED
+
+#include <vector>
+#include <numeric>
+#include <boost/assert.hpp>
+#include <boost/random/uniform_real.hpp>
+#include <boost/random/discrete_distribution.hpp>
+#include <boost/random/detail/config.hpp>
+#include <boost/random/detail/operators.hpp>
+#include <boost/random/detail/vector_io.hpp>
+
+#ifndef BOOST_NO_CXX11_HDR_INITIALIZER_LIST
+#include <initializer_list>
+#endif
+
+#include <boost/range/begin.hpp>
+#include <boost/range/end.hpp>
+
+namespace boost {
+namespace random {
+
+/**
+ * The class @c piecewise_constant_distribution models a \random_distribution.
+ */
+template<class RealType = double, class WeightType = double>
+class piecewise_constant_distribution {
+public:
+ typedef std::size_t input_type;
+ typedef RealType result_type;
+
+ class param_type {
+ public:
+
+ typedef piecewise_constant_distribution distribution_type;
+
+ /**
+ * Constructs a @c param_type object, representing a distribution
+ * that produces values uniformly distributed in the range [0, 1).
+ */
+ param_type()
+ {
+ _weights.push_back(WeightType(1));
+ _intervals.push_back(RealType(0));
+ _intervals.push_back(RealType(1));
+ }
+ /**
+ * Constructs a @c param_type object from two iterator ranges
+ * containing the interval boundaries and the interval weights.
+ * If there are less than two boundaries, then this is equivalent to
+ * the default constructor and creates a single interval, [0, 1).
+ *
+ * The values of the interval boundaries must be strictly
+ * increasing, and the number of weights must be one less than
+ * the number of interval boundaries. If there are extra
+ * weights, they are ignored.
+ */
+ template<class IntervalIter, class WeightIter>
+ param_type(IntervalIter intervals_first, IntervalIter intervals_last,
+ WeightIter weight_first)
+ : _intervals(intervals_first, intervals_last)
+ {
+ if(_intervals.size() < 2) {
+ _intervals.clear();
+ _intervals.push_back(RealType(0));
+ _intervals.push_back(RealType(1));
+ _weights.push_back(WeightType(1));
+ } else {
+ _weights.reserve(_intervals.size() - 1);
+ for(std::size_t i = 0; i < _intervals.size() - 1; ++i) {
+ _weights.push_back(*weight_first++);
+ }
+ }
+ }
+#ifndef BOOST_NO_CXX11_HDR_INITIALIZER_LIST
+ /**
+ * Constructs a @c param_type object from an
+ * initializer_list containing the interval boundaries
+ * and a unary function specifying the weights. Each
+ * weight is determined by calling the function at the
+ * midpoint of the corresponding interval.
+ *
+ * If the initializer_list contains less than two elements,
+ * this is equivalent to the default constructor and the
+ * distribution will produce values uniformly distributed
+ * in the range [0, 1).
+ */
+ template<class T, class F>
+ param_type(const std::initializer_list<T>& il, F f)
+ : _intervals(il.begin(), il.end())
+ {
+ if(_intervals.size() < 2) {
+ _intervals.clear();
+ _intervals.push_back(RealType(0));
+ _intervals.push_back(RealType(1));
+ _weights.push_back(WeightType(1));
+ } else {
+ _weights.reserve(_intervals.size() - 1);
+ for(std::size_t i = 0; i < _intervals.size() - 1; ++i) {
+ RealType midpoint = (_intervals[i] + _intervals[i + 1]) / 2;
+ _weights.push_back(f(midpoint));
+ }
+ }
+ }
+#endif
+ /**
+ * Constructs a @c param_type object from Boost.Range
+ * ranges holding the interval boundaries and the weights. If
+ * there are less than two interval boundaries, this is equivalent
+ * to the default constructor and the distribution will produce
+ * values uniformly distributed in the range [0, 1). The
+ * number of weights must be one less than the number of
+ * interval boundaries.
+ */
+ template<class IntervalRange, class WeightRange>
+ param_type(const IntervalRange& intervals_arg,
+ const WeightRange& weights_arg)
+ : _intervals(boost::begin(intervals_arg), boost::end(intervals_arg)),
+ _weights(boost::begin(weights_arg), boost::end(weights_arg))
+ {
+ if(_intervals.size() < 2) {
+ _intervals.clear();
+ _intervals.push_back(RealType(0));
+ _intervals.push_back(RealType(1));
+ _weights.push_back(WeightType(1));
+ }
+ }
+
+ /**
+ * Constructs the parameters for a distribution that approximates a
+ * function. The range of the distribution is [xmin, xmax). This
+ * range is divided into nw equally sized intervals and the weights
+ * are found by calling the unary function f on the midpoints of the
+ * intervals.
+ */
+ template<class F>
+ param_type(std::size_t nw, RealType xmin, RealType xmax, F f)
+ {
+ std::size_t n = (nw == 0) ? 1 : nw;
+ double delta = (xmax - xmin) / n;
+ BOOST_ASSERT(delta > 0);
+ for(std::size_t k = 0; k < n; ++k) {
+ _weights.push_back(f(xmin + k*delta + delta/2));
+ _intervals.push_back(xmin + k*delta);
+ }
+ _intervals.push_back(xmax);
+ }
+
+ /** Returns a vector containing the interval boundaries. */
+ std::vector<RealType> intervals() const { return _intervals; }
+
+ /**
+ * Returns a vector containing the probability densities
+ * over all the intervals of the distribution.
+ */
+ std::vector<RealType> densities() const
+ {
+ RealType sum = std::accumulate(_weights.begin(), _weights.end(),
+ static_cast<RealType>(0));
+ std::vector<RealType> result;
+ result.reserve(_weights.size());
+ for(std::size_t i = 0; i < _weights.size(); ++i) {
+ RealType width = _intervals[i + 1] - _intervals[i];
+ result.push_back(_weights[i] / (sum * width));
+ }
+ return result;
+ }
+
+ /** Writes the parameters to a @c std::ostream. */
+ BOOST_RANDOM_DETAIL_OSTREAM_OPERATOR(os, param_type, parm)
+ {
+ detail::print_vector(os, parm._intervals);
+ detail::print_vector(os, parm._weights);
+ return os;
+ }
+
+ /** Reads the parameters from a @c std::istream. */
+ BOOST_RANDOM_DETAIL_ISTREAM_OPERATOR(is, param_type, parm)
+ {
+ std::vector<RealType> new_intervals;
+ std::vector<WeightType> new_weights;
+ detail::read_vector(is, new_intervals);
+ detail::read_vector(is, new_weights);
+ if(is) {
+ parm._intervals.swap(new_intervals);
+ parm._weights.swap(new_weights);
+ }
+ return is;
+ }
+
+ /** Returns true if the two sets of parameters are the same. */
+ BOOST_RANDOM_DETAIL_EQUALITY_OPERATOR(param_type, lhs, rhs)
+ {
+ return lhs._intervals == rhs._intervals
+ && lhs._weights == rhs._weights;
+ }
+ /** Returns true if the two sets of parameters are different. */
+ BOOST_RANDOM_DETAIL_INEQUALITY_OPERATOR(param_type)
+
+ private:
+
+ friend class piecewise_constant_distribution;
+
+ std::vector<RealType> _intervals;
+ std::vector<WeightType> _weights;
+ };
+
+ /**
+ * Creates a new @c piecewise_constant_distribution with
+ * a single interval, [0, 1).
+ */
+ piecewise_constant_distribution()
+ {
+ _intervals.push_back(RealType(0));
+ _intervals.push_back(RealType(1));
+ }
+ /**
+ * Constructs a piecewise_constant_distribution from two iterator ranges
+ * containing the interval boundaries and the interval weights.
+ * If there are less than two boundaries, then this is equivalent to
+ * the default constructor and creates a single interval, [0, 1).
+ *
+ * The values of the interval boundaries must be strictly
+ * increasing, and the number of weights must be one less than
+ * the number of interval boundaries. If there are extra
+ * weights, they are ignored.
+ *
+ * For example,
+ *
+ * @code
+ * double intervals[] = { 0.0, 1.0, 4.0 };
+ * double weights[] = { 1.0, 1.0 };
+ * piecewise_constant_distribution<> dist(
+ * &intervals[0], &intervals[0] + 3, &weights[0]);
+ * @endcode
+ *
+ * The distribution has a 50% chance of producing a
+ * value between 0 and 1 and a 50% chance of producing
+ * a value between 1 and 4.
+ */
+ template<class IntervalIter, class WeightIter>
+ piecewise_constant_distribution(IntervalIter first_interval,
+ IntervalIter last_interval,
+ WeightIter first_weight)
+ : _intervals(first_interval, last_interval)
+ {
+ if(_intervals.size() < 2) {
+ _intervals.clear();
+ _intervals.push_back(RealType(0));
+ _intervals.push_back(RealType(1));
+ } else {
+ std::vector<WeightType> actual_weights;
+ actual_weights.reserve(_intervals.size() - 1);
+ for(std::size_t i = 0; i < _intervals.size() - 1; ++i) {
+ actual_weights.push_back(*first_weight++);
+ }
+ typedef discrete_distribution<std::size_t, WeightType> bins_type;
+ typename bins_type::param_type bins_param(actual_weights);
+ _bins.param(bins_param);
+ }
+ }
+#ifndef BOOST_NO_CXX11_HDR_INITIALIZER_LIST
+ /**
+ * Constructs a piecewise_constant_distribution from an
+ * initializer_list containing the interval boundaries
+ * and a unary function specifying the weights. Each
+ * weight is determined by calling the function at the
+ * midpoint of the corresponding interval.
+ *
+ * If the initializer_list contains less than two elements,
+ * this is equivalent to the default constructor and the
+ * distribution will produce values uniformly distributed
+ * in the range [0, 1).
+ */
+ template<class T, class F>
+ piecewise_constant_distribution(std::initializer_list<T> il, F f)
+ : _intervals(il.begin(), il.end())
+ {
+ if(_intervals.size() < 2) {
+ _intervals.clear();
+ _intervals.push_back(RealType(0));
+ _intervals.push_back(RealType(1));
+ } else {
+ std::vector<WeightType> actual_weights;
+ actual_weights.reserve(_intervals.size() - 1);
+ for(std::size_t i = 0; i < _intervals.size() - 1; ++i) {
+ RealType midpoint = (_intervals[i] + _intervals[i + 1]) / 2;
+ actual_weights.push_back(f(midpoint));
+ }
+ typedef discrete_distribution<std::size_t, WeightType> bins_type;
+ typename bins_type::param_type bins_param(actual_weights);
+ _bins.param(bins_param);
+ }
+ }
+#endif
+ /**
+ * Constructs a piecewise_constant_distribution from Boost.Range
+ * ranges holding the interval boundaries and the weights. If
+ * there are less than two interval boundaries, this is equivalent
+ * to the default constructor and the distribution will produce
+ * values uniformly distributed in the range [0, 1). The
+ * number of weights must be one less than the number of
+ * interval boundaries.
+ */
+ template<class IntervalsRange, class WeightsRange>
+ piecewise_constant_distribution(const IntervalsRange& intervals_arg,
+ const WeightsRange& weights_arg)
+ : _bins(weights_arg),
+ _intervals(boost::begin(intervals_arg), boost::end(intervals_arg))
+ {
+ if(_intervals.size() < 2) {
+ _intervals.clear();
+ _intervals.push_back(RealType(0));
+ _intervals.push_back(RealType(1));
+ }
+ }
+ /**
+ * Constructs a piecewise_constant_distribution that approximates a
+ * function. The range of the distribution is [xmin, xmax). This
+ * range is divided into nw equally sized intervals and the weights
+ * are found by calling the unary function f on the midpoints of the
+ * intervals.
+ */
+ template<class F>
+ piecewise_constant_distribution(std::size_t nw,
+ RealType xmin,
+ RealType xmax,
+ F f)
+ : _bins(nw, xmin, xmax, f)
+ {
+ if(nw == 0) { nw = 1; }
+ RealType delta = (xmax - xmin) / nw;
+ _intervals.reserve(nw + 1);
+ for(std::size_t i = 0; i < nw; ++i) {
+ _intervals.push_back(xmin + i * delta);
+ }
+ _intervals.push_back(xmax);
+ }
+ /**
+ * Constructs a piecewise_constant_distribution from its parameters.
+ */
+ explicit piecewise_constant_distribution(const param_type& parm)
+ : _bins(parm._weights),
+ _intervals(parm._intervals)
+ {
+ }
+
+ /**
+ * Returns a value distributed according to the parameters of the
+ * piecewist_constant_distribution.
+ */
+ template<class URNG>
+ RealType operator()(URNG& urng) const
+ {
+ std::size_t i = _bins(urng);
+ return uniform_real<RealType>(_intervals[i], _intervals[i+1])(urng);
+ }
+
+ /**
+ * Returns a value distributed according to the parameters
+ * specified by param.
+ */
+ template<class URNG>
+ RealType operator()(URNG& urng, const param_type& parm) const
+ {
+ return piecewise_constant_distribution(parm)(urng);
+ }
+
+ /** Returns the smallest value that the distribution can produce. */
+ result_type min BOOST_PREVENT_MACRO_SUBSTITUTION () const
+ { return _intervals.front(); }
+ /** Returns the largest value that the distribution can produce. */
+ result_type max BOOST_PREVENT_MACRO_SUBSTITUTION () const
+ { return _intervals.back(); }
+
+ /**
+ * Returns a vector containing the probability density
+ * over each interval.
+ */
+ std::vector<RealType> densities() const
+ {
+ std::vector<RealType> result(_bins.probabilities());
+ for(std::size_t i = 0; i < result.size(); ++i) {
+ result[i] /= (_intervals[i+1] - _intervals[i]);
+ }
+ return(result);
+ }
+ /** Returns a vector containing the interval boundaries. */
+ std::vector<RealType> intervals() const { return _intervals; }
+
+ /** Returns the parameters of the distribution. */
+ param_type param() const
+ {
+ return param_type(_intervals, _bins.probabilities());
+ }
+ /** Sets the parameters of the distribution. */
+ void param(const param_type& parm)
+ {
+ std::vector<RealType> new_intervals(parm._intervals);
+ typedef discrete_distribution<std::size_t, RealType> bins_type;
+ typename bins_type::param_type bins_param(parm._weights);
+ _bins.param(bins_param);
+ _intervals.swap(new_intervals);
+ }
+
+ /**
+ * Effects: Subsequent uses of the distribution do not depend
+ * on values produced by any engine prior to invoking reset.
+ */
+ void reset() { _bins.reset(); }
+
+ /** Writes a distribution to a @c std::ostream. */
+ BOOST_RANDOM_DETAIL_OSTREAM_OPERATOR(
+ os, piecewise_constant_distribution, pcd)
+ {
+ os << pcd.param();
+ return os;
+ }
+
+ /** Reads a distribution from a @c std::istream */
+ BOOST_RANDOM_DETAIL_ISTREAM_OPERATOR(
+ is, piecewise_constant_distribution, pcd)
+ {
+ param_type parm;
+ if(is >> parm) {
+ pcd.param(parm);
+ }
+ return is;
+ }
+
+ /**
+ * Returns true if the two distributions will return the
+ * same sequence of values, when passed equal generators.
+ */
+ BOOST_RANDOM_DETAIL_EQUALITY_OPERATOR(
+ piecewise_constant_distribution, lhs, rhs)
+ {
+ return lhs._bins == rhs._bins && lhs._intervals == rhs._intervals;
+ }
+ /**
+ * Returns true if the two distributions may return different
+ * sequences of values, when passed equal generators.
+ */
+ BOOST_RANDOM_DETAIL_INEQUALITY_OPERATOR(piecewise_constant_distribution)
+
+private:
+ discrete_distribution<std::size_t, WeightType> _bins;
+ std::vector<RealType> _intervals;
+};
+
+}
+}
+
+#endif
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