--- /dev/null
+// Special functions -*- C++ -*-
+
+// Copyright (C) 2006, 2007, 2008, 2009, 2010
+// Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library. This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+//
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// Under Section 7 of GPL version 3, you are granted additional
+// permissions described in the GCC Runtime Library Exception, version
+// 3.1, as published by the Free Software Foundation.
+
+// You should have received a copy of the GNU General Public License and
+// a copy of the GCC Runtime Library Exception along with this program;
+// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
+// <http://www.gnu.org/licenses/>.
+
+/** @file tr1/gamma.tcc
+ * This is an internal header file, included by other library headers.
+ * Do not attempt to use it directly. @headername{tr1/cmath}
+ */
+
+//
+// ISO C++ 14882 TR1: 5.2 Special functions
+//
+
+// Written by Edward Smith-Rowland based on:
+// (1) Handbook of Mathematical Functions,
+// ed. Milton Abramowitz and Irene A. Stegun,
+// Dover Publications,
+// Section 6, pp. 253-266
+// (2) The Gnu Scientific Library, http://www.gnu.org/software/gsl
+// (3) Numerical Recipes in C, by W. H. Press, S. A. Teukolsky,
+// W. T. Vetterling, B. P. Flannery, Cambridge University Press (1992),
+// 2nd ed, pp. 213-216
+// (4) Gamma, Exploring Euler's Constant, Julian Havil,
+// Princeton, 2003.
+
+#ifndef _GLIBCXX_TR1_GAMMA_TCC
+#define _GLIBCXX_TR1_GAMMA_TCC 1
+
+#include "special_function_util.h"
+
+namespace std _GLIBCXX_VISIBILITY(default)
+{
+namespace tr1
+{
+ // Implementation-space details.
+ namespace __detail
+ {
+ _GLIBCXX_BEGIN_NAMESPACE_VERSION
+
+ /**
+ * @brief This returns Bernoulli numbers from a table or by summation
+ * for larger values.
+ *
+ * Recursion is unstable.
+ *
+ * @param __n the order n of the Bernoulli number.
+ * @return The Bernoulli number of order n.
+ */
+ template <typename _Tp>
+ _Tp __bernoulli_series(unsigned int __n)
+ {
+
+ static const _Tp __num[28] = {
+ _Tp(1UL), -_Tp(1UL) / _Tp(2UL),
+ _Tp(1UL) / _Tp(6UL), _Tp(0UL),
+ -_Tp(1UL) / _Tp(30UL), _Tp(0UL),
+ _Tp(1UL) / _Tp(42UL), _Tp(0UL),
+ -_Tp(1UL) / _Tp(30UL), _Tp(0UL),
+ _Tp(5UL) / _Tp(66UL), _Tp(0UL),
+ -_Tp(691UL) / _Tp(2730UL), _Tp(0UL),
+ _Tp(7UL) / _Tp(6UL), _Tp(0UL),
+ -_Tp(3617UL) / _Tp(510UL), _Tp(0UL),
+ _Tp(43867UL) / _Tp(798UL), _Tp(0UL),
+ -_Tp(174611) / _Tp(330UL), _Tp(0UL),
+ _Tp(854513UL) / _Tp(138UL), _Tp(0UL),
+ -_Tp(236364091UL) / _Tp(2730UL), _Tp(0UL),
+ _Tp(8553103UL) / _Tp(6UL), _Tp(0UL)
+ };
+
+ if (__n == 0)
+ return _Tp(1);
+
+ if (__n == 1)
+ return -_Tp(1) / _Tp(2);
+
+ // Take care of the rest of the odd ones.
+ if (__n % 2 == 1)
+ return _Tp(0);
+
+ // Take care of some small evens that are painful for the series.
+ if (__n < 28)
+ return __num[__n];
+
+
+ _Tp __fact = _Tp(1);
+ if ((__n / 2) % 2 == 0)
+ __fact *= _Tp(-1);
+ for (unsigned int __k = 1; __k <= __n; ++__k)
+ __fact *= __k / (_Tp(2) * __numeric_constants<_Tp>::__pi());
+ __fact *= _Tp(2);
+
+ _Tp __sum = _Tp(0);
+ for (unsigned int __i = 1; __i < 1000; ++__i)
+ {
+ _Tp __term = std::pow(_Tp(__i), -_Tp(__n));
+ if (__term < std::numeric_limits<_Tp>::epsilon())
+ break;
+ __sum += __term;
+ }
+
+ return __fact * __sum;
+ }
+
+
+ /**
+ * @brief This returns Bernoulli number \f$B_n\f$.
+ *
+ * @param __n the order n of the Bernoulli number.
+ * @return The Bernoulli number of order n.
+ */
+ template<typename _Tp>
+ inline _Tp
+ __bernoulli(const int __n)
+ {
+ return __bernoulli_series<_Tp>(__n);
+ }
+
+
+ /**
+ * @brief Return \f$log(\Gamma(x))\f$ by asymptotic expansion
+ * with Bernoulli number coefficients. This is like
+ * Sterling's approximation.
+ *
+ * @param __x The argument of the log of the gamma function.
+ * @return The logarithm of the gamma function.
+ */
+ template<typename _Tp>
+ _Tp
+ __log_gamma_bernoulli(const _Tp __x)
+ {
+ _Tp __lg = (__x - _Tp(0.5L)) * std::log(__x) - __x
+ + _Tp(0.5L) * std::log(_Tp(2)
+ * __numeric_constants<_Tp>::__pi());
+
+ const _Tp __xx = __x * __x;
+ _Tp __help = _Tp(1) / __x;
+ for ( unsigned int __i = 1; __i < 20; ++__i )
+ {
+ const _Tp __2i = _Tp(2 * __i);
+ __help /= __2i * (__2i - _Tp(1)) * __xx;
+ __lg += __bernoulli<_Tp>(2 * __i) * __help;
+ }
+
+ return __lg;
+ }
+
+
+ /**
+ * @brief Return \f$log(\Gamma(x))\f$ by the Lanczos method.
+ * This method dominates all others on the positive axis I think.
+ *
+ * @param __x The argument of the log of the gamma function.
+ * @return The logarithm of the gamma function.
+ */
+ template<typename _Tp>
+ _Tp
+ __log_gamma_lanczos(const _Tp __x)
+ {
+ const _Tp __xm1 = __x - _Tp(1);
+
+ static const _Tp __lanczos_cheb_7[9] = {
+ _Tp( 0.99999999999980993227684700473478L),
+ _Tp( 676.520368121885098567009190444019L),
+ _Tp(-1259.13921672240287047156078755283L),
+ _Tp( 771.3234287776530788486528258894L),
+ _Tp(-176.61502916214059906584551354L),
+ _Tp( 12.507343278686904814458936853L),
+ _Tp(-0.13857109526572011689554707L),
+ _Tp( 9.984369578019570859563e-6L),
+ _Tp( 1.50563273514931155834e-7L)
+ };
+
+ static const _Tp __LOGROOT2PI
+ = _Tp(0.9189385332046727417803297364056176L);
+
+ _Tp __sum = __lanczos_cheb_7[0];
+ for(unsigned int __k = 1; __k < 9; ++__k)
+ __sum += __lanczos_cheb_7[__k] / (__xm1 + __k);
+
+ const _Tp __term1 = (__xm1 + _Tp(0.5L))
+ * std::log((__xm1 + _Tp(7.5L))
+ / __numeric_constants<_Tp>::__euler());
+ const _Tp __term2 = __LOGROOT2PI + std::log(__sum);
+ const _Tp __result = __term1 + (__term2 - _Tp(7));
+
+ return __result;
+ }
+
+
+ /**
+ * @brief Return \f$ log(|\Gamma(x)|) \f$.
+ * This will return values even for \f$ x < 0 \f$.
+ * To recover the sign of \f$ \Gamma(x) \f$ for
+ * any argument use @a __log_gamma_sign.
+ *
+ * @param __x The argument of the log of the gamma function.
+ * @return The logarithm of the gamma function.
+ */
+ template<typename _Tp>
+ _Tp
+ __log_gamma(const _Tp __x)
+ {
+ if (__x > _Tp(0.5L))
+ return __log_gamma_lanczos(__x);
+ else
+ {
+ const _Tp __sin_fact
+ = std::abs(std::sin(__numeric_constants<_Tp>::__pi() * __x));
+ if (__sin_fact == _Tp(0))
+ std::__throw_domain_error(__N("Argument is nonpositive integer "
+ "in __log_gamma"));
+ return __numeric_constants<_Tp>::__lnpi()
+ - std::log(__sin_fact)
+ - __log_gamma_lanczos(_Tp(1) - __x);
+ }
+ }
+
+
+ /**
+ * @brief Return the sign of \f$ \Gamma(x) \f$.
+ * At nonpositive integers zero is returned.
+ *
+ * @param __x The argument of the gamma function.
+ * @return The sign of the gamma function.
+ */
+ template<typename _Tp>
+ _Tp
+ __log_gamma_sign(const _Tp __x)
+ {
+ if (__x > _Tp(0))
+ return _Tp(1);
+ else
+ {
+ const _Tp __sin_fact
+ = std::sin(__numeric_constants<_Tp>::__pi() * __x);
+ if (__sin_fact > _Tp(0))
+ return (1);
+ else if (__sin_fact < _Tp(0))
+ return -_Tp(1);
+ else
+ return _Tp(0);
+ }
+ }
+
+
+ /**
+ * @brief Return the logarithm of the binomial coefficient.
+ * The binomial coefficient is given by:
+ * @f[
+ * \left( \right) = \frac{n!}{(n-k)! k!}
+ * @f]
+ *
+ * @param __n The first argument of the binomial coefficient.
+ * @param __k The second argument of the binomial coefficient.
+ * @return The binomial coefficient.
+ */
+ template<typename _Tp>
+ _Tp
+ __log_bincoef(const unsigned int __n, const unsigned int __k)
+ {
+ // Max e exponent before overflow.
+ static const _Tp __max_bincoeff
+ = std::numeric_limits<_Tp>::max_exponent10
+ * std::log(_Tp(10)) - _Tp(1);
+#if _GLIBCXX_USE_C99_MATH_TR1
+ _Tp __coeff = std::tr1::lgamma(_Tp(1 + __n))
+ - std::tr1::lgamma(_Tp(1 + __k))
+ - std::tr1::lgamma(_Tp(1 + __n - __k));
+#else
+ _Tp __coeff = __log_gamma(_Tp(1 + __n))
+ - __log_gamma(_Tp(1 + __k))
+ - __log_gamma(_Tp(1 + __n - __k));
+#endif
+ }
+
+
+ /**
+ * @brief Return the binomial coefficient.
+ * The binomial coefficient is given by:
+ * @f[
+ * \left( \right) = \frac{n!}{(n-k)! k!}
+ * @f]
+ *
+ * @param __n The first argument of the binomial coefficient.
+ * @param __k The second argument of the binomial coefficient.
+ * @return The binomial coefficient.
+ */
+ template<typename _Tp>
+ _Tp
+ __bincoef(const unsigned int __n, const unsigned int __k)
+ {
+ // Max e exponent before overflow.
+ static const _Tp __max_bincoeff
+ = std::numeric_limits<_Tp>::max_exponent10
+ * std::log(_Tp(10)) - _Tp(1);
+
+ const _Tp __log_coeff = __log_bincoef<_Tp>(__n, __k);
+ if (__log_coeff > __max_bincoeff)
+ return std::numeric_limits<_Tp>::quiet_NaN();
+ else
+ return std::exp(__log_coeff);
+ }
+
+
+ /**
+ * @brief Return \f$ \Gamma(x) \f$.
+ *
+ * @param __x The argument of the gamma function.
+ * @return The gamma function.
+ */
+ template<typename _Tp>
+ inline _Tp
+ __gamma(const _Tp __x)
+ {
+ return std::exp(__log_gamma(__x));
+ }
+
+
+ /**
+ * @brief Return the digamma function by series expansion.
+ * The digamma or @f$ \psi(x) @f$ function is defined by
+ * @f[
+ * \psi(x) = \frac{\Gamma'(x)}{\Gamma(x)}
+ * @f]
+ *
+ * The series is given by:
+ * @f[
+ * \psi(x) = -\gamma_E - \frac{1}{x}
+ * \sum_{k=1}^{\infty} \frac{x}{k(x + k)}
+ * @f]
+ */
+ template<typename _Tp>
+ _Tp
+ __psi_series(const _Tp __x)
+ {
+ _Tp __sum = -__numeric_constants<_Tp>::__gamma_e() - _Tp(1) / __x;
+ const unsigned int __max_iter = 100000;
+ for (unsigned int __k = 1; __k < __max_iter; ++__k)
+ {
+ const _Tp __term = __x / (__k * (__k + __x));
+ __sum += __term;
+ if (std::abs(__term / __sum) < std::numeric_limits<_Tp>::epsilon())
+ break;
+ }
+ return __sum;
+ }
+
+
+ /**
+ * @brief Return the digamma function for large argument.
+ * The digamma or @f$ \psi(x) @f$ function is defined by
+ * @f[
+ * \psi(x) = \frac{\Gamma'(x)}{\Gamma(x)}
+ * @f]
+ *
+ * The asymptotic series is given by:
+ * @f[
+ * \psi(x) = \ln(x) - \frac{1}{2x}
+ * - \sum_{n=1}^{\infty} \frac{B_{2n}}{2 n x^{2n}}
+ * @f]
+ */
+ template<typename _Tp>
+ _Tp
+ __psi_asymp(const _Tp __x)
+ {
+ _Tp __sum = std::log(__x) - _Tp(0.5L) / __x;
+ const _Tp __xx = __x * __x;
+ _Tp __xp = __xx;
+ const unsigned int __max_iter = 100;
+ for (unsigned int __k = 1; __k < __max_iter; ++__k)
+ {
+ const _Tp __term = __bernoulli<_Tp>(2 * __k) / (2 * __k * __xp);
+ __sum -= __term;
+ if (std::abs(__term / __sum) < std::numeric_limits<_Tp>::epsilon())
+ break;
+ __xp *= __xx;
+ }
+ return __sum;
+ }
+
+
+ /**
+ * @brief Return the digamma function.
+ * The digamma or @f$ \psi(x) @f$ function is defined by
+ * @f[
+ * \psi(x) = \frac{\Gamma'(x)}{\Gamma(x)}
+ * @f]
+ * For negative argument the reflection formula is used:
+ * @f[
+ * \psi(x) = \psi(1-x) - \pi \cot(\pi x)
+ * @f]
+ */
+ template<typename _Tp>
+ _Tp
+ __psi(const _Tp __x)
+ {
+ const int __n = static_cast<int>(__x + 0.5L);
+ const _Tp __eps = _Tp(4) * std::numeric_limits<_Tp>::epsilon();
+ if (__n <= 0 && std::abs(__x - _Tp(__n)) < __eps)
+ return std::numeric_limits<_Tp>::quiet_NaN();
+ else if (__x < _Tp(0))
+ {
+ const _Tp __pi = __numeric_constants<_Tp>::__pi();
+ return __psi(_Tp(1) - __x)
+ - __pi * std::cos(__pi * __x) / std::sin(__pi * __x);
+ }
+ else if (__x > _Tp(100))
+ return __psi_asymp(__x);
+ else
+ return __psi_series(__x);
+ }
+
+
+ /**
+ * @brief Return the polygamma function @f$ \psi^{(n)}(x) @f$.
+ *
+ * The polygamma function is related to the Hurwitz zeta function:
+ * @f[
+ * \psi^{(n)}(x) = (-1)^{n+1} m! \zeta(m+1,x)
+ * @f]
+ */
+ template<typename _Tp>
+ _Tp
+ __psi(const unsigned int __n, const _Tp __x)
+ {
+ if (__x <= _Tp(0))
+ std::__throw_domain_error(__N("Argument out of range "
+ "in __psi"));
+ else if (__n == 0)
+ return __psi(__x);
+ else
+ {
+ const _Tp __hzeta = __hurwitz_zeta(_Tp(__n + 1), __x);
+#if _GLIBCXX_USE_C99_MATH_TR1
+ const _Tp __ln_nfact = std::tr1::lgamma(_Tp(__n + 1));
+#else
+ const _Tp __ln_nfact = __log_gamma(_Tp(__n + 1));
+#endif
+ _Tp __result = std::exp(__ln_nfact) * __hzeta;
+ if (__n % 2 == 1)
+ __result = -__result;
+ return __result;
+ }
+ }
+
+ _GLIBCXX_END_NAMESPACE_VERSION
+ } // namespace std::tr1::__detail
+}
+}
+
+#endif // _GLIBCXX_TR1_GAMMA_TCC
+
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