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			590 lines
		
	
	
		
			22 KiB
		
	
	
	
		
			Plaintext
		
	
	
	
	
	
| //  Copyright (c) 2006 Xiaogang Zhang
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| //  Use, modification and distribution are subject to the
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| //  Boost Software License, Version 1.0. (See accompanying file
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| //  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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| 
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| #ifndef BOOST_MATH_BESSEL_JY_HPP
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| #define BOOST_MATH_BESSEL_JY_HPP
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| 
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| #ifdef _MSC_VER
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| #pragma once
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| #endif
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| 
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| #include <boost/math/tools/config.hpp>
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| #include <boost/math/special_functions/gamma.hpp>
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| #include <boost/math/special_functions/sign.hpp>
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| #include <boost/math/special_functions/hypot.hpp>
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| #include <boost/math/special_functions/sin_pi.hpp>
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| #include <boost/math/special_functions/cos_pi.hpp>
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| #include <boost/math/special_functions/detail/bessel_jy_asym.hpp>
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| #include <boost/math/special_functions/detail/bessel_jy_series.hpp>
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| #include <boost/math/constants/constants.hpp>
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| #include <boost/math/policies/error_handling.hpp>
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| #include <boost/mpl/if.hpp>
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| #include <boost/type_traits/is_floating_point.hpp>
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| #include <complex>
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| 
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| // Bessel functions of the first and second kind of fractional order
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| 
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| namespace boost { namespace math {
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| 
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|    namespace detail {
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| 
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|       //
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|       // Simultaneous calculation of A&S 9.2.9 and 9.2.10
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|       // for use in A&S 9.2.5 and 9.2.6.
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|       // This series is quick to evaluate, but divergent unless
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|       // x is very large, in fact it's pretty hard to figure out
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|       // with any degree of precision when this series actually 
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|       // *will* converge!!  Consequently, we may just have to
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|       // try it and see...
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|       //
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|       template <class T, class Policy>
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|       bool hankel_PQ(T v, T x, T* p, T* q, const Policy& )
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|       {
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|          BOOST_MATH_STD_USING
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|             T tolerance = 2 * policies::get_epsilon<T, Policy>();
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|          *p = 1;
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|          *q = 0;
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|          T k = 1;
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|          T z8 = 8 * x;
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|          T sq = 1;
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|          T mu = 4 * v * v;
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|          T term = 1;
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|          bool ok = true;
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|          do
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|          {
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|             term *= (mu - sq * sq) / (k * z8);
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|             *q += term;
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|             k += 1;
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|             sq += 2;
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|             T mult = (sq * sq - mu) / (k * z8);
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|             ok = fabs(mult) < 0.5f;
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|             term *= mult;
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|             *p += term;
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|             k += 1;
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|             sq += 2;
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|          }
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|          while((fabs(term) > tolerance * *p) && ok);
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|          return ok;
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|       }
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| 
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|       // Calculate Y(v, x) and Y(v+1, x) by Temme's method, see
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|       // Temme, Journal of Computational Physics, vol 21, 343 (1976)
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|       template <typename T, typename Policy>
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|       int temme_jy(T v, T x, T* Y, T* Y1, const Policy& pol)
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|       {
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|          T g, h, p, q, f, coef, sum, sum1, tolerance;
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|          T a, d, e, sigma;
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|          unsigned long k;
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| 
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|          BOOST_MATH_STD_USING
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|             using namespace boost::math::tools;
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|          using namespace boost::math::constants;
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| 
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|          BOOST_ASSERT(fabs(v) <= 0.5f);  // precondition for using this routine
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| 
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|          T gp = boost::math::tgamma1pm1(v, pol);
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|          T gm = boost::math::tgamma1pm1(-v, pol);
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|          T spv = boost::math::sin_pi(v, pol);
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|          T spv2 = boost::math::sin_pi(v/2, pol);
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|          T xp = pow(x/2, v);
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| 
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|          a = log(x / 2);
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|          sigma = -a * v;
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|          d = abs(sigma) < tools::epsilon<T>() ?
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|             T(1) : sinh(sigma) / sigma;
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|          e = abs(v) < tools::epsilon<T>() ? T(v*pi<T>()*pi<T>() / 2)
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|             : T(2 * spv2 * spv2 / v);
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| 
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|          T g1 = (v == 0) ? T(-euler<T>()) : T((gp - gm) / ((1 + gp) * (1 + gm) * 2 * v));
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|          T g2 = (2 + gp + gm) / ((1 + gp) * (1 + gm) * 2);
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|          T vspv = (fabs(v) < tools::epsilon<T>()) ? T(1/constants::pi<T>()) : T(v / spv);
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|          f = (g1 * cosh(sigma) - g2 * a * d) * 2 * vspv;
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| 
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|          p = vspv / (xp * (1 + gm));
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|          q = vspv * xp / (1 + gp);
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| 
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|          g = f + e * q;
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|          h = p;
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|          coef = 1;
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|          sum = coef * g;
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|          sum1 = coef * h;
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| 
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|          T v2 = v * v;
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|          T coef_mult = -x * x / 4;
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| 
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|          // series summation
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|          tolerance = policies::get_epsilon<T, Policy>();
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|          for (k = 1; k < policies::get_max_series_iterations<Policy>(); k++)
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|          {
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|             f = (k * f + p + q) / (k*k - v2);
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|             p /= k - v;
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|             q /= k + v;
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|             g = f + e * q;
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|             h = p - k * g;
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|             coef *= coef_mult / k;
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|             sum += coef * g;
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|             sum1 += coef * h;
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|             if (abs(coef * g) < abs(sum) * tolerance) 
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|             { 
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|                break; 
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|             }
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|          }
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|          policies::check_series_iterations<T>("boost::math::bessel_jy<%1%>(%1%,%1%) in temme_jy", k, pol);
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|          *Y = -sum;
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|          *Y1 = -2 * sum1 / x;
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| 
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|          return 0;
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|       }
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| 
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|       // Evaluate continued fraction fv = J_(v+1) / J_v, see
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|       // Abramowitz and Stegun, Handbook of Mathematical Functions, 1972, 9.1.73
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|       template <typename T, typename Policy>
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|       int CF1_jy(T v, T x, T* fv, int* sign, const Policy& pol)
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|       {
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|          T C, D, f, a, b, delta, tiny, tolerance;
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|          unsigned long k;
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|          int s = 1;
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| 
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|          BOOST_MATH_STD_USING
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| 
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|             // |x| <= |v|, CF1_jy converges rapidly
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|             // |x| > |v|, CF1_jy needs O(|x|) iterations to converge
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| 
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|             // modified Lentz's method, see
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|             // Lentz, Applied Optics, vol 15, 668 (1976)
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|             tolerance = 2 * policies::get_epsilon<T, Policy>();;
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|          tiny = sqrt(tools::min_value<T>());
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|          C = f = tiny;                           // b0 = 0, replace with tiny
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|          D = 0;
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|          for (k = 1; k < policies::get_max_series_iterations<Policy>() * 100; k++)
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|          {
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|             a = -1;
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|             b = 2 * (v + k) / x;
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|             C = b + a / C;
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|             D = b + a * D;
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|             if (C == 0) { C = tiny; }
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|             if (D == 0) { D = tiny; }
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|             D = 1 / D;
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|             delta = C * D;
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|             f *= delta;
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|             if (D < 0) { s = -s; }
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|             if (abs(delta - 1) < tolerance) 
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|             { break; }
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|          }
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|          policies::check_series_iterations<T>("boost::math::bessel_jy<%1%>(%1%,%1%) in CF1_jy", k / 100, pol);
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|          *fv = -f;
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|          *sign = s;                              // sign of denominator
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| 
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|          return 0;
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|       }
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|       //
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|       // This algorithm was originally written by Xiaogang Zhang
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|       // using std::complex to perform the complex arithmetic.
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|       // However, that turns out to 10x or more slower than using
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|       // all real-valued arithmetic, so it's been rewritten using
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|       // real values only.
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|       //
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|       template <typename T, typename Policy>
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|       int CF2_jy(T v, T x, T* p, T* q, const Policy& pol)
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|       {
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|          BOOST_MATH_STD_USING
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| 
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|             T Cr, Ci, Dr, Di, fr, fi, a, br, bi, delta_r, delta_i, temp;
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|          T tiny;
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|          unsigned long k;
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| 
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|          // |x| >= |v|, CF2_jy converges rapidly
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|          // |x| -> 0, CF2_jy fails to converge
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|          BOOST_ASSERT(fabs(x) > 1);
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| 
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|          // modified Lentz's method, complex numbers involved, see
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|          // Lentz, Applied Optics, vol 15, 668 (1976)
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|          T tolerance = 2 * policies::get_epsilon<T, Policy>();
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|          tiny = sqrt(tools::min_value<T>());
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|          Cr = fr = -0.5f / x;
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|          Ci = fi = 1;
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|          //Dr = Di = 0;
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|          T v2 = v * v;
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|          a = (0.25f - v2) / x; // Note complex this one time only!
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|          br = 2 * x;
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|          bi = 2;
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|          temp = Cr * Cr + 1;
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|          Ci = bi + a * Cr / temp;
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|          Cr = br + a / temp;
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|          Dr = br;
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|          Di = bi;
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|          if (fabs(Cr) + fabs(Ci) < tiny) { Cr = tiny; }
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|          if (fabs(Dr) + fabs(Di) < tiny) { Dr = tiny; }
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|          temp = Dr * Dr + Di * Di;
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|          Dr = Dr / temp;
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|          Di = -Di / temp;
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|          delta_r = Cr * Dr - Ci * Di;
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|          delta_i = Ci * Dr + Cr * Di;
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|          temp = fr;
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|          fr = temp * delta_r - fi * delta_i;
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|          fi = temp * delta_i + fi * delta_r;
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|          for (k = 2; k < policies::get_max_series_iterations<Policy>(); k++)
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|          {
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|             a = k - 0.5f;
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|             a *= a;
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|             a -= v2;
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|             bi += 2;
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|             temp = Cr * Cr + Ci * Ci;
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|             Cr = br + a * Cr / temp;
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|             Ci = bi - a * Ci / temp;
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|             Dr = br + a * Dr;
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|             Di = bi + a * Di;
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|             if (fabs(Cr) + fabs(Ci) < tiny) { Cr = tiny; }
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|             if (fabs(Dr) + fabs(Di) < tiny) { Dr = tiny; }
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|             temp = Dr * Dr + Di * Di;
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|             Dr = Dr / temp;
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|             Di = -Di / temp;
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|             delta_r = Cr * Dr - Ci * Di;
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|             delta_i = Ci * Dr + Cr * Di;
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|             temp = fr;
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|             fr = temp * delta_r - fi * delta_i;
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|             fi = temp * delta_i + fi * delta_r;
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|             if (fabs(delta_r - 1) + fabs(delta_i) < tolerance)
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|                break;
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|          }
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|          policies::check_series_iterations<T>("boost::math::bessel_jy<%1%>(%1%,%1%) in CF2_jy", k, pol);
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|          *p = fr;
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|          *q = fi;
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| 
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|          return 0;
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|       }
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| 
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|       static const int need_j = 1;
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|       static const int need_y = 2;
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| 
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|       // Compute J(v, x) and Y(v, x) simultaneously by Steed's method, see
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|       // Barnett et al, Computer Physics Communications, vol 8, 377 (1974)
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|       template <typename T, typename Policy>
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|       int bessel_jy(T v, T x, T* J, T* Y, int kind, const Policy& pol)
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|       {
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|          BOOST_ASSERT(x >= 0);
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| 
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|          T u, Jv, Ju, Yv, Yv1, Yu, Yu1(0), fv, fu;
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|          T W, p, q, gamma, current, prev, next;
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|          bool reflect = false;
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|          unsigned n, k;
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|          int s;
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|          int org_kind = kind;
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|          T cp = 0;
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|          T sp = 0;
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| 
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|          static const char* function = "boost::math::bessel_jy<%1%>(%1%,%1%)";
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| 
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|          BOOST_MATH_STD_USING
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|             using namespace boost::math::tools;
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|          using namespace boost::math::constants;
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| 
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|          if (v < 0)
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|          {
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|             reflect = true;
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|             v = -v;                             // v is non-negative from here
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|          }
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|          if (v > static_cast<T>((std::numeric_limits<int>::max)()))
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|          {
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|             *J = *Y = policies::raise_evaluation_error<T>(function, "Order of Bessel function is too large to evaluate: got %1%", v, pol);
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|             return 1;
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|          }
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|          n = iround(v, pol);
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|          u = v - n;                              // -1/2 <= u < 1/2
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| 
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|          if(reflect)
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|          {
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|             T z = (u + n % 2);
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|             cp = boost::math::cos_pi(z, pol);
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|             sp = boost::math::sin_pi(z, pol);
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|             if(u != 0)
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|                kind = need_j|need_y;               // need both for reflection formula
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|          }
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| 
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|          if(x == 0)
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|          {
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|             if(v == 0)
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|                *J = 1;
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|             else if((u == 0) || !reflect)
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|                *J = 0;
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|             else if(kind & need_j)
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|                *J = policies::raise_domain_error<T>(function, "Value of Bessel J_v(x) is complex-infinity at %1%", x, pol); // complex infinity
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|             else
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|                *J = std::numeric_limits<T>::quiet_NaN();  // any value will do, not using J.
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| 
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|             if((kind & need_y) == 0)
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|                *Y = std::numeric_limits<T>::quiet_NaN();  // any value will do, not using Y.
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|             else if(v == 0)
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|                *Y = -policies::raise_overflow_error<T>(function, 0, pol);
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|             else
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|                *Y = policies::raise_domain_error<T>(function, "Value of Bessel Y_v(x) is complex-infinity at %1%", x, pol); // complex infinity
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|             return 1;
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|          }
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| 
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|          // x is positive until reflection
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|          W = T(2) / (x * pi<T>());               // Wronskian
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|          T Yv_scale = 1;
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|          if(((kind & need_y) == 0) && ((x < 1) || (v > x * x / 4) || (x < 5)))
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|          {
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|             //
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|             // This series will actually converge rapidly for all small
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|             // x - say up to x < 20 - but the first few terms are large
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|             // and divergent which leads to large errors :-(
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|             //
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|             Jv = bessel_j_small_z_series(v, x, pol);
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|             Yv = std::numeric_limits<T>::quiet_NaN();
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|          }
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|          else if((x < 1) && (u != 0) && (log(policies::get_epsilon<T, Policy>() / 2) > v * log((x/2) * (x/2) / v)))
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|          {
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|             // Evaluate using series representations.
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|             // This is particularly important for x << v as in this
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|             // area temme_jy may be slow to converge, if it converges at all.
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|             // Requires x is not an integer.
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|             if(kind&need_j)
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|                Jv = bessel_j_small_z_series(v, x, pol);
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|             else
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|                Jv = std::numeric_limits<T>::quiet_NaN();
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|             if((org_kind&need_y && (!reflect || (cp != 0))) 
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|                || (org_kind & need_j && (reflect && (sp != 0))))
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|             {
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|                // Only calculate if we need it, and if the reflection formula will actually use it:
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|                Yv = bessel_y_small_z_series(v, x, &Yv_scale, pol);
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|             }
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|             else
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|                Yv = std::numeric_limits<T>::quiet_NaN();
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|          }
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|          else if((u == 0) && (x < policies::get_epsilon<T, Policy>()))
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|          {
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|             // Truncated series evaluation for small x and v an integer,
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|             // much quicker in this area than temme_jy below.
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|             if(kind&need_j)
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|                Jv = bessel_j_small_z_series(v, x, pol);
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|             else
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|                Jv = std::numeric_limits<T>::quiet_NaN();
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|             if((org_kind&need_y && (!reflect || (cp != 0))) 
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|                || (org_kind & need_j && (reflect && (sp != 0))))
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|             {
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|                // Only calculate if we need it, and if the reflection formula will actually use it:
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|                Yv = bessel_yn_small_z(n, x, &Yv_scale, pol);
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|             }
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|             else
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|                Yv = std::numeric_limits<T>::quiet_NaN();
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|          }
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|          else if(asymptotic_bessel_large_x_limit(v, x))
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|          {
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|             if(kind&need_y)
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|             {
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|                Yv = asymptotic_bessel_y_large_x_2(v, x);
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|             }
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|             else
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|                Yv = std::numeric_limits<T>::quiet_NaN(); // any value will do, we're not using it.
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|             if(kind&need_j)
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|             {
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|                Jv = asymptotic_bessel_j_large_x_2(v, x);
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|             }
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|             else
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|                Jv = std::numeric_limits<T>::quiet_NaN(); // any value will do, we're not using it.
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|          }
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|          else if((x > 8) && hankel_PQ(v, x, &p, &q, pol))
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|          {
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|             //
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|             // Hankel approximation: note that this method works best when x 
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|             // is large, but in that case we end up calculating sines and cosines
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|             // of large values, with horrendous resulting accuracy.  It is fast though
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|             // when it works....
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|             //
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|             // Normally we calculate sin/cos(chi) where:
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|             //
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|             // chi = x - fmod(T(v / 2 + 0.25f), T(2)) * boost::math::constants::pi<T>();
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|             //
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|             // But this introduces large errors, so use sin/cos addition formulae to
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|             // improve accuracy:
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|             //
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|             T mod_v = fmod(T(v / 2 + 0.25f), T(2));
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|             T sx = sin(x);
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|             T cx = cos(x);
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|             T sv = sin_pi(mod_v);
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|             T cv = cos_pi(mod_v);
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| 
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|             T sc = sx * cv - sv * cx; // == sin(chi);
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|             T cc = cx * cv + sx * sv; // == cos(chi);
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|             T chi = boost::math::constants::root_two<T>() / (boost::math::constants::root_pi<T>() * sqrt(x)); //sqrt(2 / (boost::math::constants::pi<T>() * x));
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|             Yv = chi * (p * sc + q * cc);
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|             Jv = chi * (p * cc - q * sc);
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|          }
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|          else if (x <= 2)                           // x in (0, 2]
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|          {
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|             if(temme_jy(u, x, &Yu, &Yu1, pol))             // Temme series
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|             {
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|                // domain error:
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|                *J = *Y = Yu;
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|                return 1;
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|             }
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|             prev = Yu;
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|             current = Yu1;
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|             T scale = 1;
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|             policies::check_series_iterations<T>(function, n, pol);
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|             for (k = 1; k <= n; k++)            // forward recurrence for Y
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|             {
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|                T fact = 2 * (u + k) / x;
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|                if((tools::max_value<T>() - fabs(prev)) / fact < fabs(current))
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|                {
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|                   scale /= current;
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|                   prev /= current;
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|                   current = 1;
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|                }
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|                next = fact * current - prev;
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|                prev = current;
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|                current = next;
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|             }
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|             Yv = prev;
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|             Yv1 = current;
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|             if(kind&need_j)
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|             {
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|                CF1_jy(v, x, &fv, &s, pol);                 // continued fraction CF1_jy
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|                Jv = scale * W / (Yv * fv - Yv1);           // Wronskian relation
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|             }
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|             else
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|                Jv = std::numeric_limits<T>::quiet_NaN(); // any value will do, we're not using it.
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|             Yv_scale = scale;
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|          }
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|          else                                    // x in (2, \infty)
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|          {
 | |
|             // Get Y(u, x):
 | |
| 
 | |
|             T ratio;
 | |
|             CF1_jy(v, x, &fv, &s, pol);
 | |
|             // tiny initial value to prevent overflow
 | |
|             T init = sqrt(tools::min_value<T>());
 | |
|             BOOST_MATH_INSTRUMENT_VARIABLE(init);
 | |
|             prev = fv * s * init;
 | |
|             current = s * init;
 | |
|             if(v < max_factorial<T>::value)
 | |
|             {
 | |
|                policies::check_series_iterations<T>(function, n, pol);
 | |
|                for (k = n; k > 0; k--)             // backward recurrence for J
 | |
|                {
 | |
|                   next = 2 * (u + k) * current / x - prev;
 | |
|                   prev = current;
 | |
|                   current = next;
 | |
|                }
 | |
|                ratio = (s * init) / current;     // scaling ratio
 | |
|                // can also call CF1_jy() to get fu, not much difference in precision
 | |
|                fu = prev / current;
 | |
|             }
 | |
|             else
 | |
|             {
 | |
|                //
 | |
|                // When v is large we may get overflow in this calculation
 | |
|                // leading to NaN's and other nasty surprises:
 | |
|                //
 | |
|                policies::check_series_iterations<T>(function, n, pol);
 | |
|                bool over = false;
 | |
|                for (k = n; k > 0; k--)             // backward recurrence for J
 | |
|                {
 | |
|                   T t = 2 * (u + k) / x;
 | |
|                   if((t > 1) && (tools::max_value<T>() / t < current))
 | |
|                   {
 | |
|                      over = true;
 | |
|                      break;
 | |
|                   }
 | |
|                   next = t * current - prev;
 | |
|                   prev = current;
 | |
|                   current = next;
 | |
|                }
 | |
|                if(!over)
 | |
|                {
 | |
|                   ratio = (s * init) / current;     // scaling ratio
 | |
|                   // can also call CF1_jy() to get fu, not much difference in precision
 | |
|                   fu = prev / current;
 | |
|                }
 | |
|                else
 | |
|                {
 | |
|                   ratio = 0;
 | |
|                   fu = 1;
 | |
|                }
 | |
|             }
 | |
|             CF2_jy(u, x, &p, &q, pol);                  // continued fraction CF2_jy
 | |
|             T t = u / x - fu;                   // t = J'/J
 | |
|             gamma = (p - t) / q;
 | |
|             //
 | |
|             // We can't allow gamma to cancel out to zero competely as it messes up
 | |
|             // the subsequent logic.  So pretend that one bit didn't cancel out
 | |
|             // and set to a suitably small value.  The only test case we've been able to
 | |
|             // find for this, is when v = 8.5 and x = 4*PI.
 | |
|             //
 | |
|             if(gamma == 0)
 | |
|             {
 | |
|                gamma = u * tools::epsilon<T>() / x;
 | |
|             }
 | |
|             BOOST_MATH_INSTRUMENT_VARIABLE(current);
 | |
|             BOOST_MATH_INSTRUMENT_VARIABLE(W);
 | |
|             BOOST_MATH_INSTRUMENT_VARIABLE(q);
 | |
|             BOOST_MATH_INSTRUMENT_VARIABLE(gamma);
 | |
|             BOOST_MATH_INSTRUMENT_VARIABLE(p);
 | |
|             BOOST_MATH_INSTRUMENT_VARIABLE(t);
 | |
|             Ju = sign(current) * sqrt(W / (q + gamma * (p - t)));
 | |
|             BOOST_MATH_INSTRUMENT_VARIABLE(Ju);
 | |
| 
 | |
|             Jv = Ju * ratio;                    // normalization
 | |
| 
 | |
|             Yu = gamma * Ju;
 | |
|             Yu1 = Yu * (u/x - p - q/gamma);
 | |
| 
 | |
|             if(kind&need_y)
 | |
|             {
 | |
|                // compute Y:
 | |
|                prev = Yu;
 | |
|                current = Yu1;
 | |
|                policies::check_series_iterations<T>(function, n, pol);
 | |
|                for (k = 1; k <= n; k++)            // forward recurrence for Y
 | |
|                {
 | |
|                   T fact = 2 * (u + k) / x;
 | |
|                   if((tools::max_value<T>() - fabs(prev)) / fact < fabs(current))
 | |
|                   {
 | |
|                      prev /= current;
 | |
|                      Yv_scale /= current;
 | |
|                      current = 1;
 | |
|                   }
 | |
|                   next = fact * current - prev;
 | |
|                   prev = current;
 | |
|                   current = next;
 | |
|                }
 | |
|                Yv = prev;
 | |
|             }
 | |
|             else
 | |
|                Yv = std::numeric_limits<T>::quiet_NaN(); // any value will do, we're not using it.
 | |
|          }
 | |
| 
 | |
|          if (reflect)
 | |
|          {
 | |
|             if((sp != 0) && (tools::max_value<T>() * fabs(Yv_scale) < fabs(sp * Yv)))
 | |
|                *J = org_kind & need_j ? T(-sign(sp) * sign(Yv) * sign(Yv_scale) * policies::raise_overflow_error<T>(function, 0, pol)) : T(0);
 | |
|             else
 | |
|                *J = cp * Jv - (sp == 0 ? T(0) : T((sp * Yv) / Yv_scale));     // reflection formula
 | |
|             if((cp != 0) && (tools::max_value<T>() * fabs(Yv_scale) < fabs(cp * Yv)))
 | |
|                *Y = org_kind & need_y ? T(-sign(cp) * sign(Yv) * sign(Yv_scale) * policies::raise_overflow_error<T>(function, 0, pol)) : T(0);
 | |
|             else
 | |
|                *Y = (sp != 0 ? sp * Jv : T(0)) + (cp == 0 ? T(0) : T((cp * Yv) / Yv_scale));
 | |
|          }
 | |
|          else
 | |
|          {
 | |
|             *J = Jv;
 | |
|             if(tools::max_value<T>() * fabs(Yv_scale) < fabs(Yv))
 | |
|                *Y = org_kind & need_y ? T(sign(Yv) * sign(Yv_scale) * policies::raise_overflow_error<T>(function, 0, pol)) : T(0);
 | |
|             else
 | |
|                *Y = Yv / Yv_scale;
 | |
|          }
 | |
| 
 | |
|          return 0;
 | |
|       }
 | |
| 
 | |
|    } // namespace detail
 | |
| 
 | |
| }} // namespaces
 | |
| 
 | |
| #endif // BOOST_MATH_BESSEL_JY_HPP
 | |
| 
 | 
