1 // Copyright (c) 2006 Xiaogang Zhang
2 // Copyright (c) 2006 John Maddock
3 // Use, modification and distribution are subject to the
4 // Boost Software License, Version 1.0. (See accompanying file
5 // LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
8 // XZ wrote the original of this file as part of the Google
9 // Summer of Code 2006. JM modified it to fit into the
10 // Boost.Math conceptual framework better, and to ensure
11 // that the code continues to work no matter how many digits
14 #ifndef BOOST_MATH_ELLINT_2_HPP
15 #define BOOST_MATH_ELLINT_2_HPP
21 #include <boost/math/special_functions/ellint_rf.hpp>
22 #include <boost/math/special_functions/ellint_rd.hpp>
23 #include <boost/math/constants/constants.hpp>
24 #include <boost/math/policies/error_handling.hpp>
25 #include <boost/math/tools/workaround.hpp>
26 #include <boost/math/special_functions/round.hpp>
28 // Elliptic integrals (complete and incomplete) of the second kind
29 // Carlson, Numerische Mathematik, vol 33, 1 (1979)
31 namespace boost { namespace math {
33 template <class T1, class T2, class Policy>
34 typename tools::promote_args<T1, T2>::type ellint_2(T1 k, T2 phi, const Policy& pol);
38 template <typename T, typename Policy>
39 T ellint_e_imp(T k, const Policy& pol);
41 // Elliptic integral (Legendre form) of the second kind
42 template <typename T, typename Policy>
43 T ellint_e_imp(T phi, T k, const Policy& pol)
46 using namespace boost::math::tools;
47 using namespace boost::math::constants;
58 if(phi >= tools::max_value<T>())
60 // Need to handle infinity as a special case:
61 result = policies::raise_overflow_error<T>("boost::math::ellint_e<%1%>(%1%,%1%)", 0, pol);
63 else if(phi > 1 / tools::epsilon<T>())
65 // Phi is so large that phi%pi is necessarily zero (or garbage),
66 // just return the second part of the duplication formula:
67 result = 2 * phi * ellint_e_imp(k, pol) / constants::pi<T>();
71 // Carlson's algorithm works only for |phi| <= pi/2,
72 // use the integrand's periodicity to normalize phi
74 // Xiaogang's original code used a cast to long long here
75 // but that fails if T has more digits than a long long,
76 // so rewritten to use fmod instead:
78 T rphi = boost::math::tools::fmod_workaround(phi, T(constants::half_pi<T>()));
79 T m = boost::math::round((phi - rphi) / constants::half_pi<T>());
81 if(boost::math::tools::fmod_workaround(m, T(2)) > 0.5)
85 rphi = constants::half_pi<T>() - rphi;
90 T t = k * k * sinp * sinp;
93 result = s * sinp * (ellint_rf_imp(x, y, z, pol) - t * ellint_rd_imp(x, y, z, pol) / 3);
95 result += m * ellint_e_imp(k, pol);
97 return invert ? T(-result) : result;
100 // Complete elliptic integral (Legendre form) of the second kind
101 template <typename T, typename Policy>
102 T ellint_e_imp(T k, const Policy& pol)
105 using namespace boost::math::tools;
109 return policies::raise_domain_error<T>("boost::math::ellint_e<%1%>(%1%)",
110 "Got k = %1%, function requires |k| <= 1", k, pol);
114 return static_cast<T>(1);
121 T value = ellint_rf_imp(x, y, z, pol) - t * ellint_rd_imp(x, y, z, pol) / 3;
126 template <typename T, typename Policy>
127 inline typename tools::promote_args<T>::type ellint_2(T k, const Policy& pol, const mpl::true_&)
129 typedef typename tools::promote_args<T>::type result_type;
130 typedef typename policies::evaluation<result_type, Policy>::type value_type;
131 return policies::checked_narrowing_cast<result_type, Policy>(detail::ellint_e_imp(static_cast<value_type>(k), pol), "boost::math::ellint_2<%1%>(%1%)");
134 // Elliptic integral (Legendre form) of the second kind
135 template <class T1, class T2>
136 inline typename tools::promote_args<T1, T2>::type ellint_2(T1 k, T2 phi, const mpl::false_&)
138 return boost::math::ellint_2(k, phi, policies::policy<>());
143 // Complete elliptic integral (Legendre form) of the second kind
144 template <typename T>
145 inline typename tools::promote_args<T>::type ellint_2(T k)
147 return ellint_2(k, policies::policy<>());
150 // Elliptic integral (Legendre form) of the second kind
151 template <class T1, class T2>
152 inline typename tools::promote_args<T1, T2>::type ellint_2(T1 k, T2 phi)
154 typedef typename policies::is_policy<T2>::type tag_type;
155 return detail::ellint_2(k, phi, tag_type());
158 template <class T1, class T2, class Policy>
159 inline typename tools::promote_args<T1, T2>::type ellint_2(T1 k, T2 phi, const Policy& pol)
161 typedef typename tools::promote_args<T1, T2>::type result_type;
162 typedef typename policies::evaluation<result_type, Policy>::type value_type;
163 return policies::checked_narrowing_cast<result_type, Policy>(detail::ellint_e_imp(static_cast<value_type>(phi), static_cast<value_type>(k), pol), "boost::math::ellint_2<%1%>(%1%,%1%)");
168 #endif // BOOST_MATH_ELLINT_2_HPP