| // Copyright (c) 2006 Xiaogang Zhang |
| // Use, modification and distribution are subject to 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) |
| |
| #ifndef BOOST_MATH_BESSEL_KN_HPP |
| #define BOOST_MATH_BESSEL_KN_HPP |
| |
| #ifdef _MSC_VER |
| #pragma once |
| #endif |
| |
| #include <boost/math/special_functions/detail/bessel_k0.hpp> |
| #include <boost/math/special_functions/detail/bessel_k1.hpp> |
| #include <boost/math/policies/error_handling.hpp> |
| |
| // Modified Bessel function of the second kind of integer order |
| // K_n(z) is the dominant solution, forward recurrence always OK (though unstable) |
| |
| namespace boost { namespace math { namespace detail{ |
| |
| template <typename T, typename Policy> |
| T bessel_kn(int n, T x, const Policy& pol) |
| { |
| T value, current, prev; |
| |
| using namespace boost::math::tools; |
| |
| static const char* function = "boost::math::bessel_kn<%1%>(%1%,%1%)"; |
| |
| if (x < 0) |
| { |
| return policies::raise_domain_error<T>(function, |
| "Got x = %1%, but argument x must be non-negative, complex number result not supported.", x, pol); |
| } |
| if (x == 0) |
| { |
| return policies::raise_overflow_error<T>(function, 0, pol); |
| } |
| |
| if (n < 0) |
| { |
| n = -n; // K_{-n}(z) = K_n(z) |
| } |
| if (n == 0) |
| { |
| value = bessel_k0(x, pol); |
| } |
| else if (n == 1) |
| { |
| value = bessel_k1(x, pol); |
| } |
| else |
| { |
| prev = bessel_k0(x, pol); |
| current = bessel_k1(x, pol); |
| int k = 1; |
| BOOST_ASSERT(k < n); |
| do |
| { |
| value = 2 * k * current / x + prev; |
| prev = current; |
| current = value; |
| ++k; |
| } |
| while(k < n); |
| } |
| return value; |
| } |
| |
| }}} // namespaces |
| |
| #endif // BOOST_MATH_BESSEL_KN_HPP |
| |