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/* boost random/triangle_distribution.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: triangle_distribution.hpp 71018 2011-04-05 21:27:52Z steven_watanabe $
*
* Revision history
* 2001-02-18 moved to individual header files
*/
#ifndef BOOST_RANDOM_TRIANGLE_DISTRIBUTION_HPP
#define BOOST_RANDOM_TRIANGLE_DISTRIBUTION_HPP
#include <boost/config/no_tr1/cmath.hpp>
#include <iosfwd>
#include <ios>
#include <istream>
#include <boost/assert.hpp>
#include <boost/random/detail/config.hpp>
#include <boost/random/detail/operators.hpp>
#include <boost/random/uniform_01.hpp>
namespace boost {
namespace random {
/**
* Instantiations of @c triangle_distribution model a \random_distribution.
* A @c triangle_distribution has three parameters, @c a, @c b, and @c c,
* which are the smallest, the most probable and the largest values of
* the distribution respectively.
*/
template<class RealType = double>
class triangle_distribution
{
public:
typedef RealType input_type;
typedef RealType result_type;
class param_type
{
public:
typedef triangle_distribution distribution_type;
/** Constructs the parameters of a @c triangle_distribution. */
explicit param_type(RealType a_arg = RealType(0.0),
RealType b_arg = RealType(0.5),
RealType c_arg = RealType(1.0))
: _a(a_arg), _b(b_arg), _c(c_arg)
{
BOOST_ASSERT(_a <= _b && _b <= _c);
}
/** Returns the minimum value of the distribution. */
RealType a() const { return _a; }
/** Returns the mode of the distribution. */
RealType b() const { return _b; }
/** Returns the maximum value of the distribution. */
RealType c() const { return _c; }
/** Writes the parameters to a @c std::ostream. */
BOOST_RANDOM_DETAIL_OSTREAM_OPERATOR(os, param_type, parm)
{
os << parm._a << " " << parm._b << " " << parm._c;
return os;
}
/** Reads the parameters from a @c std::istream. */
BOOST_RANDOM_DETAIL_ISTREAM_OPERATOR(is, param_type, parm)
{
double a_in, b_in, c_in;
if(is >> a_in >> std::ws >> b_in >> std::ws >> c_in) {
if(a_in <= b_in && b_in <= c_in) {
parm._a = a_in;
parm._b = b_in;
parm._c = c_in;
} else {
is.setstate(std::ios_base::failbit);
}
}
return is;
}
/** Returns true if the two sets of parameters are equal. */
BOOST_RANDOM_DETAIL_EQUALITY_OPERATOR(param_type, lhs, rhs)
{ return lhs._a == rhs._a && lhs._b == rhs._b && lhs._c == rhs._c; }
/** Returns true if the two sets of parameters are different. */
BOOST_RANDOM_DETAIL_INEQUALITY_OPERATOR(param_type)
private:
RealType _a;
RealType _b;
RealType _c;
};
/**
* Constructs a @c triangle_distribution with the parameters
* @c a, @c b, and @c c.
*
* Preconditions: a <= b <= c.
*/
explicit triangle_distribution(RealType a_arg = RealType(0.0),
RealType b_arg = RealType(0.5),
RealType c_arg = RealType(1.0))
: _a(a_arg), _b(b_arg), _c(c_arg)
{
BOOST_ASSERT(_a <= _b && _b <= _c);
init();
}
/** Constructs a @c triangle_distribution from its parameters. */
explicit triangle_distribution(const param_type& parm)
: _a(parm.a()), _b(parm.b()), _c(parm.c())
{
init();
}
// compiler-generated copy ctor and assignment operator are fine
/** Returns the @c a parameter of the distribution */
result_type a() const { return _a; }
/** Returns the @c b parameter of the distribution */
result_type b() const { return _b; }
/** Returns the @c c parameter of the distribution */
result_type c() const { return _c; }
/** Returns the smallest value that the distribution can produce. */
RealType min BOOST_PREVENT_MACRO_SUBSTITUTION () const { return _a; }
/** Returns the largest value that the distribution can produce. */
RealType max BOOST_PREVENT_MACRO_SUBSTITUTION () const { return _c; }
/** Returns the parameters of the distribution. */
param_type param() const { return param_type(_a, _b, _c); }
/** Sets the parameters of the distribution. */
void param(const param_type& parm)
{
_a = parm.a();
_b = parm.b();
_c = parm.c();
init();
}
/**
* Effects: Subsequent uses of the distribution do not depend
* on values produced by any engine prior to invoking reset.
*/
void reset() { }
/**
* Returns a random variate distributed according to the
* triangle distribution.
*/
template<class Engine>
result_type operator()(Engine& eng)
{
using std::sqrt;
result_type u = uniform_01<>()(eng);
if( u <= q1 )
return _a + p1*sqrt(u);
else
return _c - d3*sqrt(d2*u-d1);
}
/**
* Returns a random variate distributed according to the
* triangle distribution with parameters specified by param.
*/
template<class Engine>
result_type operator()(Engine& eng, const param_type& parm)
{ return triangle_distribution(parm)(eng); }
/** Writes the distribution to a @c std::ostream. */
BOOST_RANDOM_DETAIL_OSTREAM_OPERATOR(os, triangle_distribution, td)
{
os << td.param();
return os;
}
/** Reads the distribution from a @c std::istream. */
BOOST_RANDOM_DETAIL_ISTREAM_OPERATOR(is, triangle_distribution, td)
{
param_type parm;
if(is >> parm) {
td.param(parm);
}
return is;
}
/**
* Returns true if the two distributions will produce identical
* sequences of values given equal generators.
*/
BOOST_RANDOM_DETAIL_EQUALITY_OPERATOR(triangle_distribution, lhs, rhs)
{ return lhs._a == rhs._a && lhs._b == rhs._b && lhs._c == rhs._c; }
/**
* Returns true if the two distributions may produce different
* sequences of values given equal generators.
*/
BOOST_RANDOM_DETAIL_INEQUALITY_OPERATOR(triangle_distribution)
private:
/// \cond show_private
void init()
{
using std::sqrt;
d1 = _b - _a;
d2 = _c - _a;
d3 = sqrt(_c - _b);
q1 = d1 / d2;
p1 = sqrt(d1 * d2);
}
/// \endcond
RealType _a, _b, _c;
RealType d1, d2, d3, q1, p1;
};
} // namespace random
using random::triangle_distribution;
} // namespace boost
#endif // BOOST_RANDOM_TRIANGLE_DISTRIBUTION_HPP
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