786 lines
27 KiB
C++
786 lines
27 KiB
C++
// Special functions -*- C++ -*-
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// Copyright (C) 2006-2020 Free Software Foundation, Inc.
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//
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// This file is part of the GNU ISO C++ Library. This library is free
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// software; you can redistribute it and/or modify it under the
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// terms of the GNU General Public License as published by the
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// Free Software Foundation; either version 3, or (at your option)
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// any later version.
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//
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// This library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// Under Section 7 of GPL version 3, you are granted additional
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// permissions described in the GCC Runtime Library Exception, version
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// 3.1, as published by the Free Software Foundation.
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// You should have received a copy of the GNU General Public License and
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// a copy of the GCC Runtime Library Exception along with this program;
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// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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// <http://www.gnu.org/licenses/>.
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/** @file tr1/hypergeometric.tcc
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* This is an internal header file, included by other library headers.
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* Do not attempt to use it directly. @headername{tr1/cmath}
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*/
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//
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// ISO C++ 14882 TR1: 5.2 Special functions
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//
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// Written by Edward Smith-Rowland based:
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// (1) Handbook of Mathematical Functions,
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// ed. Milton Abramowitz and Irene A. Stegun,
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// Dover Publications,
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// Section 6, pp. 555-566
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// (2) The Gnu Scientific Library, http://www.gnu.org/software/gsl
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#ifndef _GLIBCXX_TR1_HYPERGEOMETRIC_TCC
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#define _GLIBCXX_TR1_HYPERGEOMETRIC_TCC 1
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namespace std _GLIBCXX_VISIBILITY(default)
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{
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_GLIBCXX_BEGIN_NAMESPACE_VERSION
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#if _GLIBCXX_USE_STD_SPEC_FUNCS
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# define _GLIBCXX_MATH_NS ::std
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#elif defined(_GLIBCXX_TR1_CMATH)
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namespace tr1
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{
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# define _GLIBCXX_MATH_NS ::std::tr1
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#else
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# error do not include this header directly, use <cmath> or <tr1/cmath>
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#endif
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// [5.2] Special functions
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// Implementation-space details.
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namespace __detail
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{
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/**
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* @brief This routine returns the confluent hypergeometric function
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* by series expansion.
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*
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* @f[
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* _1F_1(a;c;x) = \frac{\Gamma(c)}{\Gamma(a)}
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* \sum_{n=0}^{\infty}
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* \frac{\Gamma(a+n)}{\Gamma(c+n)}
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* \frac{x^n}{n!}
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* @f]
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*
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* If a and b are integers and a < 0 and either b > 0 or b < a
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* then the series is a polynomial with a finite number of
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* terms. If b is an integer and b <= 0 the confluent
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* hypergeometric function is undefined.
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*
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* @param __a The "numerator" parameter.
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* @param __c The "denominator" parameter.
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* @param __x The argument of the confluent hypergeometric function.
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* @return The confluent hypergeometric function.
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*/
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template<typename _Tp>
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_Tp
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__conf_hyperg_series(_Tp __a, _Tp __c, _Tp __x)
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{
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const _Tp __eps = std::numeric_limits<_Tp>::epsilon();
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_Tp __term = _Tp(1);
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_Tp __Fac = _Tp(1);
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const unsigned int __max_iter = 100000;
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unsigned int __i;
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for (__i = 0; __i < __max_iter; ++__i)
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{
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__term *= (__a + _Tp(__i)) * __x
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/ ((__c + _Tp(__i)) * _Tp(1 + __i));
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if (std::abs(__term) < __eps)
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{
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break;
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}
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__Fac += __term;
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}
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if (__i == __max_iter)
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std::__throw_runtime_error(__N("Series failed to converge "
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"in __conf_hyperg_series."));
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return __Fac;
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}
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/**
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* @brief Return the hypogeometric function @f$ _2F_1(a,b;c;x) @f$
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* by an iterative procedure described in
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* Luke, Algorithms for the Computation of Mathematical Functions.
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*
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* Like the case of the 2F1 rational approximations, these are
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* probably guaranteed to converge for x < 0, barring gross
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* numerical instability in the pre-asymptotic regime.
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*/
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template<typename _Tp>
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_Tp
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__conf_hyperg_luke(_Tp __a, _Tp __c, _Tp __xin)
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{
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const _Tp __big = std::pow(std::numeric_limits<_Tp>::max(), _Tp(0.16L));
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const int __nmax = 20000;
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const _Tp __eps = std::numeric_limits<_Tp>::epsilon();
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const _Tp __x = -__xin;
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const _Tp __x3 = __x * __x * __x;
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const _Tp __t0 = __a / __c;
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const _Tp __t1 = (__a + _Tp(1)) / (_Tp(2) * __c);
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const _Tp __t2 = (__a + _Tp(2)) / (_Tp(2) * (__c + _Tp(1)));
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_Tp __F = _Tp(1);
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_Tp __prec;
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_Tp __Bnm3 = _Tp(1);
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_Tp __Bnm2 = _Tp(1) + __t1 * __x;
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_Tp __Bnm1 = _Tp(1) + __t2 * __x * (_Tp(1) + __t1 / _Tp(3) * __x);
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_Tp __Anm3 = _Tp(1);
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_Tp __Anm2 = __Bnm2 - __t0 * __x;
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_Tp __Anm1 = __Bnm1 - __t0 * (_Tp(1) + __t2 * __x) * __x
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+ __t0 * __t1 * (__c / (__c + _Tp(1))) * __x * __x;
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int __n = 3;
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while(1)
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{
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_Tp __npam1 = _Tp(__n - 1) + __a;
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_Tp __npcm1 = _Tp(__n - 1) + __c;
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_Tp __npam2 = _Tp(__n - 2) + __a;
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_Tp __npcm2 = _Tp(__n - 2) + __c;
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_Tp __tnm1 = _Tp(2 * __n - 1);
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_Tp __tnm3 = _Tp(2 * __n - 3);
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_Tp __tnm5 = _Tp(2 * __n - 5);
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_Tp __F1 = (_Tp(__n - 2) - __a) / (_Tp(2) * __tnm3 * __npcm1);
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_Tp __F2 = (_Tp(__n) + __a) * __npam1
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/ (_Tp(4) * __tnm1 * __tnm3 * __npcm2 * __npcm1);
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_Tp __F3 = -__npam2 * __npam1 * (_Tp(__n - 2) - __a)
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/ (_Tp(8) * __tnm3 * __tnm3 * __tnm5
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* (_Tp(__n - 3) + __c) * __npcm2 * __npcm1);
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_Tp __E = -__npam1 * (_Tp(__n - 1) - __c)
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/ (_Tp(2) * __tnm3 * __npcm2 * __npcm1);
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_Tp __An = (_Tp(1) + __F1 * __x) * __Anm1
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+ (__E + __F2 * __x) * __x * __Anm2 + __F3 * __x3 * __Anm3;
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_Tp __Bn = (_Tp(1) + __F1 * __x) * __Bnm1
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+ (__E + __F2 * __x) * __x * __Bnm2 + __F3 * __x3 * __Bnm3;
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_Tp __r = __An / __Bn;
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__prec = std::abs((__F - __r) / __F);
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__F = __r;
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if (__prec < __eps || __n > __nmax)
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break;
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if (std::abs(__An) > __big || std::abs(__Bn) > __big)
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{
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__An /= __big;
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__Bn /= __big;
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__Anm1 /= __big;
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__Bnm1 /= __big;
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__Anm2 /= __big;
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__Bnm2 /= __big;
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__Anm3 /= __big;
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__Bnm3 /= __big;
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}
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else if (std::abs(__An) < _Tp(1) / __big
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|| std::abs(__Bn) < _Tp(1) / __big)
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{
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__An *= __big;
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__Bn *= __big;
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__Anm1 *= __big;
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__Bnm1 *= __big;
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__Anm2 *= __big;
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__Bnm2 *= __big;
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__Anm3 *= __big;
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__Bnm3 *= __big;
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}
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++__n;
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__Bnm3 = __Bnm2;
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__Bnm2 = __Bnm1;
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__Bnm1 = __Bn;
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__Anm3 = __Anm2;
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__Anm2 = __Anm1;
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__Anm1 = __An;
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}
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if (__n >= __nmax)
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std::__throw_runtime_error(__N("Iteration failed to converge "
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"in __conf_hyperg_luke."));
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return __F;
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}
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/**
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* @brief Return the confluent hypogeometric function
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* @f$ _1F_1(a;c;x) @f$.
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*
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* @todo Handle b == nonpositive integer blowup - return NaN.
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*
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* @param __a The @a numerator parameter.
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* @param __c The @a denominator parameter.
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* @param __x The argument of the confluent hypergeometric function.
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* @return The confluent hypergeometric function.
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*/
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template<typename _Tp>
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_Tp
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__conf_hyperg(_Tp __a, _Tp __c, _Tp __x)
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{
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#if _GLIBCXX_USE_C99_MATH_TR1
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const _Tp __c_nint = _GLIBCXX_MATH_NS::nearbyint(__c);
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#else
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const _Tp __c_nint = static_cast<int>(__c + _Tp(0.5L));
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#endif
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if (__isnan(__a) || __isnan(__c) || __isnan(__x))
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return std::numeric_limits<_Tp>::quiet_NaN();
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else if (__c_nint == __c && __c_nint <= 0)
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return std::numeric_limits<_Tp>::infinity();
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else if (__a == _Tp(0))
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return _Tp(1);
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else if (__c == __a)
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return std::exp(__x);
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else if (__x < _Tp(0))
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return __conf_hyperg_luke(__a, __c, __x);
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else
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return __conf_hyperg_series(__a, __c, __x);
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}
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/**
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* @brief Return the hypogeometric function @f$ _2F_1(a,b;c;x) @f$
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* by series expansion.
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*
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* The hypogeometric function is defined by
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* @f[
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* _2F_1(a,b;c;x) = \frac{\Gamma(c)}{\Gamma(a)\Gamma(b)}
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* \sum_{n=0}^{\infty}
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* \frac{\Gamma(a+n)\Gamma(b+n)}{\Gamma(c+n)}
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* \frac{x^n}{n!}
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* @f]
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*
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* This works and it's pretty fast.
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*
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* @param __a The first @a numerator parameter.
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* @param __a The second @a numerator parameter.
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* @param __c The @a denominator parameter.
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* @param __x The argument of the confluent hypergeometric function.
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* @return The confluent hypergeometric function.
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*/
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template<typename _Tp>
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_Tp
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__hyperg_series(_Tp __a, _Tp __b, _Tp __c, _Tp __x)
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{
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const _Tp __eps = std::numeric_limits<_Tp>::epsilon();
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_Tp __term = _Tp(1);
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_Tp __Fabc = _Tp(1);
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const unsigned int __max_iter = 100000;
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unsigned int __i;
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for (__i = 0; __i < __max_iter; ++__i)
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{
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__term *= (__a + _Tp(__i)) * (__b + _Tp(__i)) * __x
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/ ((__c + _Tp(__i)) * _Tp(1 + __i));
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if (std::abs(__term) < __eps)
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{
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break;
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}
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__Fabc += __term;
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}
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if (__i == __max_iter)
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std::__throw_runtime_error(__N("Series failed to converge "
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"in __hyperg_series."));
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return __Fabc;
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}
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/**
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* @brief Return the hypogeometric function @f$ _2F_1(a,b;c;x) @f$
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* by an iterative procedure described in
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* Luke, Algorithms for the Computation of Mathematical Functions.
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*/
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template<typename _Tp>
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_Tp
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__hyperg_luke(_Tp __a, _Tp __b, _Tp __c, _Tp __xin)
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{
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const _Tp __big = std::pow(std::numeric_limits<_Tp>::max(), _Tp(0.16L));
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const int __nmax = 20000;
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const _Tp __eps = std::numeric_limits<_Tp>::epsilon();
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const _Tp __x = -__xin;
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const _Tp __x3 = __x * __x * __x;
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const _Tp __t0 = __a * __b / __c;
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const _Tp __t1 = (__a + _Tp(1)) * (__b + _Tp(1)) / (_Tp(2) * __c);
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const _Tp __t2 = (__a + _Tp(2)) * (__b + _Tp(2))
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/ (_Tp(2) * (__c + _Tp(1)));
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_Tp __F = _Tp(1);
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_Tp __Bnm3 = _Tp(1);
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_Tp __Bnm2 = _Tp(1) + __t1 * __x;
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_Tp __Bnm1 = _Tp(1) + __t2 * __x * (_Tp(1) + __t1 / _Tp(3) * __x);
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_Tp __Anm3 = _Tp(1);
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_Tp __Anm2 = __Bnm2 - __t0 * __x;
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_Tp __Anm1 = __Bnm1 - __t0 * (_Tp(1) + __t2 * __x) * __x
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+ __t0 * __t1 * (__c / (__c + _Tp(1))) * __x * __x;
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int __n = 3;
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while (1)
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{
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const _Tp __npam1 = _Tp(__n - 1) + __a;
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const _Tp __npbm1 = _Tp(__n - 1) + __b;
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const _Tp __npcm1 = _Tp(__n - 1) + __c;
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const _Tp __npam2 = _Tp(__n - 2) + __a;
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const _Tp __npbm2 = _Tp(__n - 2) + __b;
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const _Tp __npcm2 = _Tp(__n - 2) + __c;
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const _Tp __tnm1 = _Tp(2 * __n - 1);
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const _Tp __tnm3 = _Tp(2 * __n - 3);
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const _Tp __tnm5 = _Tp(2 * __n - 5);
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const _Tp __n2 = __n * __n;
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const _Tp __F1 = (_Tp(3) * __n2 + (__a + __b - _Tp(6)) * __n
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+ _Tp(2) - __a * __b - _Tp(2) * (__a + __b))
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/ (_Tp(2) * __tnm3 * __npcm1);
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const _Tp __F2 = -(_Tp(3) * __n2 - (__a + __b + _Tp(6)) * __n
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+ _Tp(2) - __a * __b) * __npam1 * __npbm1
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/ (_Tp(4) * __tnm1 * __tnm3 * __npcm2 * __npcm1);
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const _Tp __F3 = (__npam2 * __npam1 * __npbm2 * __npbm1
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* (_Tp(__n - 2) - __a) * (_Tp(__n - 2) - __b))
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/ (_Tp(8) * __tnm3 * __tnm3 * __tnm5
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* (_Tp(__n - 3) + __c) * __npcm2 * __npcm1);
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const _Tp __E = -__npam1 * __npbm1 * (_Tp(__n - 1) - __c)
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/ (_Tp(2) * __tnm3 * __npcm2 * __npcm1);
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_Tp __An = (_Tp(1) + __F1 * __x) * __Anm1
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+ (__E + __F2 * __x) * __x * __Anm2 + __F3 * __x3 * __Anm3;
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_Tp __Bn = (_Tp(1) + __F1 * __x) * __Bnm1
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+ (__E + __F2 * __x) * __x * __Bnm2 + __F3 * __x3 * __Bnm3;
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const _Tp __r = __An / __Bn;
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const _Tp __prec = std::abs((__F - __r) / __F);
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__F = __r;
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if (__prec < __eps || __n > __nmax)
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break;
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if (std::abs(__An) > __big || std::abs(__Bn) > __big)
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{
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__An /= __big;
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__Bn /= __big;
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__Anm1 /= __big;
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__Bnm1 /= __big;
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__Anm2 /= __big;
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__Bnm2 /= __big;
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__Anm3 /= __big;
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__Bnm3 /= __big;
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}
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else if (std::abs(__An) < _Tp(1) / __big
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|| std::abs(__Bn) < _Tp(1) / __big)
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{
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__An *= __big;
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__Bn *= __big;
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__Anm1 *= __big;
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__Bnm1 *= __big;
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__Anm2 *= __big;
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__Bnm2 *= __big;
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__Anm3 *= __big;
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__Bnm3 *= __big;
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}
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++__n;
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__Bnm3 = __Bnm2;
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__Bnm2 = __Bnm1;
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__Bnm1 = __Bn;
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__Anm3 = __Anm2;
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__Anm2 = __Anm1;
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__Anm1 = __An;
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}
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if (__n >= __nmax)
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std::__throw_runtime_error(__N("Iteration failed to converge "
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"in __hyperg_luke."));
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return __F;
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}
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/**
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* @brief Return the hypogeometric function @f$ _2F_1(a,b;c;x) @f$
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* by the reflection formulae in Abramowitz & Stegun formula
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* 15.3.6 for d = c - a - b not integral and formula 15.3.11 for
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* d = c - a - b integral. This assumes a, b, c != negative
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* integer.
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*
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* The hypogeometric function is defined by
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* @f[
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* _2F_1(a,b;c;x) = \frac{\Gamma(c)}{\Gamma(a)\Gamma(b)}
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* \sum_{n=0}^{\infty}
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* \frac{\Gamma(a+n)\Gamma(b+n)}{\Gamma(c+n)}
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* \frac{x^n}{n!}
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* @f]
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*
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* The reflection formula for nonintegral @f$ d = c - a - b @f$ is:
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* @f[
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* _2F_1(a,b;c;x) = \frac{\Gamma(c)\Gamma(d)}{\Gamma(c-a)\Gamma(c-b)}
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* _2F_1(a,b;1-d;1-x)
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* + \frac{\Gamma(c)\Gamma(-d)}{\Gamma(a)\Gamma(b)}
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* _2F_1(c-a,c-b;1+d;1-x)
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* @f]
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*
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* The reflection formula for integral @f$ m = c - a - b @f$ is:
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* @f[
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* _2F_1(a,b;a+b+m;x) = \frac{\Gamma(m)\Gamma(a+b+m)}{\Gamma(a+m)\Gamma(b+m)}
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* \sum_{k=0}^{m-1} \frac{(m+a)_k(m+b)_k}{k!(1-m)_k}
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* -
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* @f]
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*/
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template<typename _Tp>
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_Tp
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__hyperg_reflect(_Tp __a, _Tp __b, _Tp __c, _Tp __x)
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{
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const _Tp __d = __c - __a - __b;
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const int __intd = std::floor(__d + _Tp(0.5L));
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const _Tp __eps = std::numeric_limits<_Tp>::epsilon();
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const _Tp __toler = _Tp(1000) * __eps;
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const _Tp __log_max = std::log(std::numeric_limits<_Tp>::max());
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const bool __d_integer = (std::abs(__d - __intd) < __toler);
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if (__d_integer)
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{
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const _Tp __ln_omx = std::log(_Tp(1) - __x);
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const _Tp __ad = std::abs(__d);
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_Tp __F1, __F2;
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_Tp __d1, __d2;
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if (__d >= _Tp(0))
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{
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__d1 = __d;
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__d2 = _Tp(0);
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}
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else
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{
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__d1 = _Tp(0);
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__d2 = __d;
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}
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const _Tp __lng_c = __log_gamma(__c);
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// Evaluate F1.
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if (__ad < __eps)
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{
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// d = c - a - b = 0.
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__F1 = _Tp(0);
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}
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else
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{
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bool __ok_d1 = true;
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_Tp __lng_ad, __lng_ad1, __lng_bd1;
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__try
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{
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__lng_ad = __log_gamma(__ad);
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__lng_ad1 = __log_gamma(__a + __d1);
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__lng_bd1 = __log_gamma(__b + __d1);
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}
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__catch(...)
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{
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__ok_d1 = false;
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}
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if (__ok_d1)
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{
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/* Gamma functions in the denominator are ok.
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* Proceed with evaluation.
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*/
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_Tp __sum1 = _Tp(1);
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_Tp __term = _Tp(1);
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_Tp __ln_pre1 = __lng_ad + __lng_c + __d2 * __ln_omx
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- __lng_ad1 - __lng_bd1;
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/* Do F1 sum.
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*/
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for (int __i = 1; __i < __ad; ++__i)
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{
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const int __j = __i - 1;
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__term *= (__a + __d2 + __j) * (__b + __d2 + __j)
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/ (_Tp(1) + __d2 + __j) / __i * (_Tp(1) - __x);
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__sum1 += __term;
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}
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if (__ln_pre1 > __log_max)
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std::__throw_runtime_error(__N("Overflow of gamma functions"
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" in __hyperg_luke."));
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else
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__F1 = std::exp(__ln_pre1) * __sum1;
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}
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else
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{
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// Gamma functions in the denominator were not ok.
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// So the F1 term is zero.
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__F1 = _Tp(0);
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}
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} // end F1 evaluation
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// Evaluate F2.
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bool __ok_d2 = true;
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_Tp __lng_ad2, __lng_bd2;
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__try
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{
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__lng_ad2 = __log_gamma(__a + __d2);
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__lng_bd2 = __log_gamma(__b + __d2);
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}
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__catch(...)
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{
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__ok_d2 = false;
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}
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if (__ok_d2)
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{
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// Gamma functions in the denominator are ok.
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// Proceed with evaluation.
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const int __maxiter = 2000;
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const _Tp __psi_1 = -__numeric_constants<_Tp>::__gamma_e();
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const _Tp __psi_1pd = __psi(_Tp(1) + __ad);
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const _Tp __psi_apd1 = __psi(__a + __d1);
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const _Tp __psi_bpd1 = __psi(__b + __d1);
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_Tp __psi_term = __psi_1 + __psi_1pd - __psi_apd1
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- __psi_bpd1 - __ln_omx;
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_Tp __fact = _Tp(1);
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_Tp __sum2 = __psi_term;
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_Tp __ln_pre2 = __lng_c + __d1 * __ln_omx
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- __lng_ad2 - __lng_bd2;
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// Do F2 sum.
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int __j;
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for (__j = 1; __j < __maxiter; ++__j)
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{
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// Values for psi functions use recurrence;
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// Abramowitz & Stegun 6.3.5
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const _Tp __term1 = _Tp(1) / _Tp(__j)
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+ _Tp(1) / (__ad + __j);
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const _Tp __term2 = _Tp(1) / (__a + __d1 + _Tp(__j - 1))
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+ _Tp(1) / (__b + __d1 + _Tp(__j - 1));
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__psi_term += __term1 - __term2;
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__fact *= (__a + __d1 + _Tp(__j - 1))
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* (__b + __d1 + _Tp(__j - 1))
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/ ((__ad + __j) * __j) * (_Tp(1) - __x);
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const _Tp __delta = __fact * __psi_term;
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__sum2 += __delta;
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if (std::abs(__delta) < __eps * std::abs(__sum2))
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break;
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}
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if (__j == __maxiter)
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std::__throw_runtime_error(__N("Sum F2 failed to converge "
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"in __hyperg_reflect"));
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if (__sum2 == _Tp(0))
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__F2 = _Tp(0);
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else
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__F2 = std::exp(__ln_pre2) * __sum2;
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}
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else
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{
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// Gamma functions in the denominator not ok.
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// So the F2 term is zero.
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__F2 = _Tp(0);
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} // end F2 evaluation
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const _Tp __sgn_2 = (__intd % 2 == 1 ? -_Tp(1) : _Tp(1));
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const _Tp __F = __F1 + __sgn_2 * __F2;
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return __F;
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}
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else
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{
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// d = c - a - b not an integer.
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// These gamma functions appear in the denominator, so we
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// catch their harmless domain errors and set the terms to zero.
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bool __ok1 = true;
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_Tp __sgn_g1ca = _Tp(0), __ln_g1ca = _Tp(0);
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_Tp __sgn_g1cb = _Tp(0), __ln_g1cb = _Tp(0);
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__try
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{
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__sgn_g1ca = __log_gamma_sign(__c - __a);
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__ln_g1ca = __log_gamma(__c - __a);
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__sgn_g1cb = __log_gamma_sign(__c - __b);
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__ln_g1cb = __log_gamma(__c - __b);
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}
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__catch(...)
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{
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__ok1 = false;
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}
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bool __ok2 = true;
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_Tp __sgn_g2a = _Tp(0), __ln_g2a = _Tp(0);
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_Tp __sgn_g2b = _Tp(0), __ln_g2b = _Tp(0);
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__try
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{
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__sgn_g2a = __log_gamma_sign(__a);
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__ln_g2a = __log_gamma(__a);
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__sgn_g2b = __log_gamma_sign(__b);
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__ln_g2b = __log_gamma(__b);
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}
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__catch(...)
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{
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__ok2 = false;
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}
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const _Tp __sgn_gc = __log_gamma_sign(__c);
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const _Tp __ln_gc = __log_gamma(__c);
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const _Tp __sgn_gd = __log_gamma_sign(__d);
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const _Tp __ln_gd = __log_gamma(__d);
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const _Tp __sgn_gmd = __log_gamma_sign(-__d);
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const _Tp __ln_gmd = __log_gamma(-__d);
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const _Tp __sgn1 = __sgn_gc * __sgn_gd * __sgn_g1ca * __sgn_g1cb;
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const _Tp __sgn2 = __sgn_gc * __sgn_gmd * __sgn_g2a * __sgn_g2b;
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_Tp __pre1, __pre2;
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if (__ok1 && __ok2)
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{
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_Tp __ln_pre1 = __ln_gc + __ln_gd - __ln_g1ca - __ln_g1cb;
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_Tp __ln_pre2 = __ln_gc + __ln_gmd - __ln_g2a - __ln_g2b
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+ __d * std::log(_Tp(1) - __x);
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if (__ln_pre1 < __log_max && __ln_pre2 < __log_max)
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{
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__pre1 = std::exp(__ln_pre1);
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__pre2 = std::exp(__ln_pre2);
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__pre1 *= __sgn1;
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__pre2 *= __sgn2;
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}
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else
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{
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std::__throw_runtime_error(__N("Overflow of gamma functions "
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"in __hyperg_reflect"));
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}
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}
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else if (__ok1 && !__ok2)
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{
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_Tp __ln_pre1 = __ln_gc + __ln_gd - __ln_g1ca - __ln_g1cb;
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if (__ln_pre1 < __log_max)
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{
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__pre1 = std::exp(__ln_pre1);
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__pre1 *= __sgn1;
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__pre2 = _Tp(0);
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}
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else
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{
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std::__throw_runtime_error(__N("Overflow of gamma functions "
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"in __hyperg_reflect"));
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}
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}
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else if (!__ok1 && __ok2)
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{
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_Tp __ln_pre2 = __ln_gc + __ln_gmd - __ln_g2a - __ln_g2b
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+ __d * std::log(_Tp(1) - __x);
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if (__ln_pre2 < __log_max)
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{
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__pre1 = _Tp(0);
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__pre2 = std::exp(__ln_pre2);
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__pre2 *= __sgn2;
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}
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else
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{
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std::__throw_runtime_error(__N("Overflow of gamma functions "
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"in __hyperg_reflect"));
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}
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}
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else
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{
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__pre1 = _Tp(0);
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__pre2 = _Tp(0);
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std::__throw_runtime_error(__N("Underflow of gamma functions "
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"in __hyperg_reflect"));
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}
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const _Tp __F1 = __hyperg_series(__a, __b, _Tp(1) - __d,
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_Tp(1) - __x);
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const _Tp __F2 = __hyperg_series(__c - __a, __c - __b, _Tp(1) + __d,
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_Tp(1) - __x);
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const _Tp __F = __pre1 * __F1 + __pre2 * __F2;
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return __F;
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}
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}
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/**
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* @brief Return the hypogeometric function @f$ _2F_1(a,b;c;x) @f$.
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*
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* The hypogeometric function is defined by
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* @f[
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* _2F_1(a,b;c;x) = \frac{\Gamma(c)}{\Gamma(a)\Gamma(b)}
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* \sum_{n=0}^{\infty}
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* \frac{\Gamma(a+n)\Gamma(b+n)}{\Gamma(c+n)}
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* \frac{x^n}{n!}
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* @f]
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*
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* @param __a The first @a numerator parameter.
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* @param __a The second @a numerator parameter.
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* @param __c The @a denominator parameter.
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* @param __x The argument of the confluent hypergeometric function.
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* @return The confluent hypergeometric function.
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*/
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template<typename _Tp>
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_Tp
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__hyperg(_Tp __a, _Tp __b, _Tp __c, _Tp __x)
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{
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#if _GLIBCXX_USE_C99_MATH_TR1
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const _Tp __a_nint = _GLIBCXX_MATH_NS::nearbyint(__a);
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const _Tp __b_nint = _GLIBCXX_MATH_NS::nearbyint(__b);
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const _Tp __c_nint = _GLIBCXX_MATH_NS::nearbyint(__c);
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#else
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const _Tp __a_nint = static_cast<int>(__a + _Tp(0.5L));
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const _Tp __b_nint = static_cast<int>(__b + _Tp(0.5L));
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const _Tp __c_nint = static_cast<int>(__c + _Tp(0.5L));
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#endif
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const _Tp __toler = _Tp(1000) * std::numeric_limits<_Tp>::epsilon();
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if (std::abs(__x) >= _Tp(1))
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std::__throw_domain_error(__N("Argument outside unit circle "
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"in __hyperg."));
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else if (__isnan(__a) || __isnan(__b)
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|| __isnan(__c) || __isnan(__x))
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return std::numeric_limits<_Tp>::quiet_NaN();
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else if (__c_nint == __c && __c_nint <= _Tp(0))
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return std::numeric_limits<_Tp>::infinity();
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else if (std::abs(__c - __b) < __toler || std::abs(__c - __a) < __toler)
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return std::pow(_Tp(1) - __x, __c - __a - __b);
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else if (__a >= _Tp(0) && __b >= _Tp(0) && __c >= _Tp(0)
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&& __x >= _Tp(0) && __x < _Tp(0.995L))
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return __hyperg_series(__a, __b, __c, __x);
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else if (std::abs(__a) < _Tp(10) && std::abs(__b) < _Tp(10))
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{
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// For integer a and b the hypergeometric function is a
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// finite polynomial.
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if (__a < _Tp(0) && std::abs(__a - __a_nint) < __toler)
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return __hyperg_series(__a_nint, __b, __c, __x);
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else if (__b < _Tp(0) && std::abs(__b - __b_nint) < __toler)
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return __hyperg_series(__a, __b_nint, __c, __x);
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else if (__x < -_Tp(0.25L))
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return __hyperg_luke(__a, __b, __c, __x);
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else if (__x < _Tp(0.5L))
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return __hyperg_series(__a, __b, __c, __x);
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else
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if (std::abs(__c) > _Tp(10))
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return __hyperg_series(__a, __b, __c, __x);
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else
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return __hyperg_reflect(__a, __b, __c, __x);
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}
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else
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return __hyperg_luke(__a, __b, __c, __x);
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}
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} // namespace __detail
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#undef _GLIBCXX_MATH_NS
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#if ! _GLIBCXX_USE_STD_SPEC_FUNCS && defined(_GLIBCXX_TR1_CMATH)
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} // namespace tr1
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#endif
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_GLIBCXX_END_NAMESPACE_VERSION
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}
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#endif // _GLIBCXX_TR1_HYPERGEOMETRIC_TCC
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