194 lines
8.3 KiB
Plaintext
194 lines
8.3 KiB
Plaintext
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// 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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#ifndef BOOST_MATH_BESSEL_J0_HPP
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#define BOOST_MATH_BESSEL_J0_HPP
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#ifdef _MSC_VER
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#pragma once
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#endif
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#include <boost/math/constants/constants.hpp>
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#include <boost/math/tools/rational.hpp>
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#include <boost/math/tools/big_constant.hpp>
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#include <boost/assert.hpp>
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// Bessel function of the first kind of order zero
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// x <= 8, minimax rational approximations on root-bracketing intervals
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// x > 8, Hankel asymptotic expansion in Hart, Computer Approximations, 1968
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namespace boost { namespace math { namespace detail{
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template <typename T>
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T bessel_j0(T x);
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template <class T>
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struct bessel_j0_initializer
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{
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struct init
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{
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init()
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{
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do_init();
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}
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static void do_init()
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{
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bessel_j0(T(1));
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}
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void force_instantiate()const{}
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};
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static const init initializer;
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static void force_instantiate()
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{
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initializer.force_instantiate();
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}
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};
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template <class T>
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const typename bessel_j0_initializer<T>::init bessel_j0_initializer<T>::initializer;
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template <typename T>
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T bessel_j0(T x)
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{
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bessel_j0_initializer<T>::force_instantiate();
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static const T P1[] = {
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, -4.1298668500990866786e+11)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 2.7282507878605942706e+10)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, -6.2140700423540120665e+08)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 6.6302997904833794242e+06)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, -3.6629814655107086448e+04)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 1.0344222815443188943e+02)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, -1.2117036164593528341e-01))
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};
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static const T Q1[] = {
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 2.3883787996332290397e+12)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 2.6328198300859648632e+10)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 1.3985097372263433271e+08)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 4.5612696224219938200e+05)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 9.3614022392337710626e+02)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 1.0)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 0.0))
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};
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static const T P2[] = {
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, -1.8319397969392084011e+03)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, -1.2254078161378989535e+04)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, -7.2879702464464618998e+03)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 1.0341910641583726701e+04)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 1.1725046279757103576e+04)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 4.4176707025325087628e+03)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 7.4321196680624245801e+02)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 4.8591703355916499363e+01))
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};
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static const T Q2[] = {
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, -3.5783478026152301072e+05)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 2.4599102262586308984e+05)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, -8.4055062591169562211e+04)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 1.8680990008359188352e+04)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, -2.9458766545509337327e+03)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 3.3307310774649071172e+02)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, -2.5258076240801555057e+01)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 1.0))
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};
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static const T PC[] = {
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 2.2779090197304684302e+04)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 4.1345386639580765797e+04)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 2.1170523380864944322e+04)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 3.4806486443249270347e+03)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 1.5376201909008354296e+02)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 8.8961548424210455236e-01))
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};
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static const T QC[] = {
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 2.2779090197304684318e+04)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 4.1370412495510416640e+04)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 2.1215350561880115730e+04)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 3.5028735138235608207e+03)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 1.5711159858080893649e+02)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 1.0))
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};
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static const T PS[] = {
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, -8.9226600200800094098e+01)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, -1.8591953644342993800e+02)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, -1.1183429920482737611e+02)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, -2.2300261666214198472e+01)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, -1.2441026745835638459e+00)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, -8.8033303048680751817e-03))
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};
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static const T QS[] = {
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 5.7105024128512061905e+03)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 1.1951131543434613647e+04)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 7.2642780169211018836e+03)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 1.4887231232283756582e+03)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 9.0593769594993125859e+01)),
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static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 1.0))
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};
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static const T x1 = static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 2.4048255576957727686e+00)),
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x2 = static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 5.5200781102863106496e+00)),
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x11 = static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 6.160e+02)),
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x12 = static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, -1.42444230422723137837e-03)),
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x21 = static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 1.4130e+03)),
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x22 = static_cast<T>(BOOST_MATH_BIG_CONSTANT(T, 64, 5.46860286310649596604e-04));
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T value, factor, r, rc, rs;
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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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if (x < 0)
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{
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x = -x; // even function
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}
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if (x == 0)
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{
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return static_cast<T>(1);
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}
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if (x <= 4) // x in (0, 4]
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{
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T y = x * x;
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BOOST_ASSERT(sizeof(P1) == sizeof(Q1));
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r = evaluate_rational(P1, Q1, y);
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factor = (x + x1) * ((x - x11/256) - x12);
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value = factor * r;
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}
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else if (x <= 8.0) // x in (4, 8]
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{
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T y = 1 - (x * x)/64;
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BOOST_ASSERT(sizeof(P2) == sizeof(Q2));
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r = evaluate_rational(P2, Q2, y);
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factor = (x + x2) * ((x - x21/256) - x22);
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value = factor * r;
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}
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else // x in (8, \infty)
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{
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T y = 8 / x;
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T y2 = y * y;
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BOOST_ASSERT(sizeof(PC) == sizeof(QC));
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BOOST_ASSERT(sizeof(PS) == sizeof(QS));
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rc = evaluate_rational(PC, QC, y2);
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rs = evaluate_rational(PS, QS, y2);
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factor = constants::one_div_root_pi<T>() / sqrt(x);
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//
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// What follows is really just:
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//
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// T z = x - pi/4;
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// value = factor * (rc * cos(z) - y * rs * sin(z));
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//
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// But using the addition formulae for sin and cos, plus
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// the special values for sin/cos of pi/4.
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//
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T sx = sin(x);
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T cx = cos(x);
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value = factor * (rc * (cx + sx) - y * rs * (sx - cx));
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}
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return value;
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}
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}}} // namespaces
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#endif // BOOST_MATH_BESSEL_J0_HPP
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