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