/* boost random/triangle_distribution.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: triangle_distribution.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_TRIANGLE_DISTRIBUTION_HPP

#define BOOST_RANDOM_TRIANGLE_DISTRIBUTION_HPP

#include <cmath>

#include <cassert>

#include <boost/random/uniform_01.hpp>

namespace boost {

// triangle distribution, with a smallest, b most probable, and c largest

// value.

template<class RealType = double>

class triangle_distribution

{

public:

  typedef RealType input_type;

  typedef RealType result_type;

  explicit triangle_distribution(result_type a = result_type(0),

                                 result_type b = result_type(0.5),

                                 result_type c = result_type(1))

    : _a(a), _b(b), _c(c)

  {

    assert(_a <= _b && _b <= _c);

    init();

  }

  // compiler-generated copy ctor and assignment operator are fine

  result_type a() const { return _a; }

  result_type b() const { return _b; }

  result_type c() const { return _c; }

  void reset() { }

  template<class Engine>

  result_type operator()(Engine& eng)

  {

#ifndef BOOST_NO_STDC_NAMESPACE

    using std::sqrt;

#endif

    result_type u = eng();

    if( u <= q1 )

      return _a + p1*sqrt(u);

    else

      return _c - d3*sqrt(d2*u-d1);

  }

#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 triangle_distribution& td)

  {

    os << td._a << " " << td._b << " " << td._c;

    return os;

  }

  template<class CharT, class Traits>

  friend std::basic_istream<CharT,Traits>&

  operator>>(std::basic_istream<CharT,Traits>& is, triangle_distribution& td)

  {

    is >> std::ws >> td._a >> std::ws >> td._b >> std::ws >> td._c;

    td.init();

    return is;

  }

#endif

private:

  void init()

  {

#ifndef BOOST_NO_STDC_NAMESPACE

    using std::sqrt;

#endif

    d1 = _b - _a;

    d2 = _c - _a;

    d3 = sqrt(_c - _b);

    q1 = d1 / d2;

    p1 = sqrt(d1 * d2);

  }

  result_type _a, _b, _c;

  result_type d1, d2, d3, q1, p1;

};

} // namespace boost

#endif // BOOST_RANDOM_TRIANGLE_DISTRIBUTION_HPP