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Diffstat (limited to 'unsupported/Eigen/src/SpecialFunctions/SpecialFunctionsImpl.h')
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diff --git a/unsupported/Eigen/src/SpecialFunctions/SpecialFunctionsImpl.h b/unsupported/Eigen/src/SpecialFunctions/SpecialFunctionsImpl.h new file mode 100644 index 000000000..f524d7137 --- /dev/null +++ b/unsupported/Eigen/src/SpecialFunctions/SpecialFunctionsImpl.h @@ -0,0 +1,1565 @@ +// This file is part of Eigen, a lightweight C++ template library +// for linear algebra. +// +// Copyright (C) 2015 Eugene Brevdo <ebrevdo@gmail.com> +// +// This Source Code Form is subject to the terms of the Mozilla +// Public License v. 2.0. If a copy of the MPL was not distributed +// with this file, You can obtain one at http://mozilla.org/MPL/2.0/. + +#ifndef EIGEN_SPECIAL_FUNCTIONS_H +#define EIGEN_SPECIAL_FUNCTIONS_H + +namespace Eigen { +namespace internal { + +// Parts of this code are based on the Cephes Math Library. +// +// Cephes Math Library Release 2.8: June, 2000 +// Copyright 1984, 1987, 1992, 2000 by Stephen L. Moshier +// +// Permission has been kindly provided by the original author +// to incorporate the Cephes software into the Eigen codebase: +// +// From: Stephen Moshier +// To: Eugene Brevdo +// Subject: Re: Permission to wrap several cephes functions in Eigen +// +// Hello Eugene, +// +// Thank you for writing. +// +// If your licensing is similar to BSD, the formal way that has been +// handled is simply to add a statement to the effect that you are incorporating +// the Cephes software by permission of the author. +// +// Good luck with your project, +// Steve + +namespace cephes { + +/* polevl (modified for Eigen) + * + * Evaluate polynomial + * + * + * + * SYNOPSIS: + * + * int N; + * Scalar x, y, coef[N+1]; + * + * y = polevl<decltype(x), N>( x, coef); + * + * + * + * DESCRIPTION: + * + * Evaluates polynomial of degree N: + * + * 2 N + * y = C + C x + C x +...+ C x + * 0 1 2 N + * + * Coefficients are stored in reverse order: + * + * coef[0] = C , ..., coef[N] = C . + * N 0 + * + * The function p1evl() assumes that coef[N] = 1.0 and is + * omitted from the array. Its calling arguments are + * otherwise the same as polevl(). + * + * + * The Eigen implementation is templatized. For best speed, store + * coef as a const array (constexpr), e.g. + * + * const double coef[] = {1.0, 2.0, 3.0, ...}; + * + */ +template <typename Scalar, int N> +struct polevl { + EIGEN_DEVICE_FUNC + static EIGEN_STRONG_INLINE Scalar run(const Scalar x, const Scalar coef[]) { + EIGEN_STATIC_ASSERT((N > 0), YOU_MADE_A_PROGRAMMING_MISTAKE); + + return polevl<Scalar, N - 1>::run(x, coef) * x + coef[N]; + } +}; + +template <typename Scalar> +struct polevl<Scalar, 0> { + EIGEN_DEVICE_FUNC + static EIGEN_STRONG_INLINE Scalar run(const Scalar, const Scalar coef[]) { + return coef[0]; + } +}; + +} // end namespace cephes + +/**************************************************************************** + * Implementation of lgamma, requires C++11/C99 * + ****************************************************************************/ + +template <typename Scalar> +struct lgamma_impl { + EIGEN_DEVICE_FUNC + static EIGEN_STRONG_INLINE Scalar run(const Scalar) { + EIGEN_STATIC_ASSERT((internal::is_same<Scalar, Scalar>::value == false), + THIS_TYPE_IS_NOT_SUPPORTED); + return Scalar(0); + } +}; + +template <typename Scalar> +struct lgamma_retval { + typedef Scalar type; +}; + +#if EIGEN_HAS_C99_MATH +template <> +struct lgamma_impl<float> { + EIGEN_DEVICE_FUNC + static EIGEN_STRONG_INLINE float run(float x) { +#if !defined(__CUDA_ARCH__) && (defined(_BSD_SOURCE) || defined(_SVID_SOURCE)) && !defined(__APPLE__) + int signgam; + return ::lgammaf_r(x, &signgam); +#else + return ::lgammaf(x); +#endif + } +}; + +template <> +struct lgamma_impl<double> { + EIGEN_DEVICE_FUNC + static EIGEN_STRONG_INLINE double run(double x) { +#if !defined(__CUDA_ARCH__) && (defined(_BSD_SOURCE) || defined(_SVID_SOURCE)) && !defined(__APPLE__) + int signgam; + return ::lgamma_r(x, &signgam); +#else + return ::lgamma(x); +#endif + } +}; +#endif + +/**************************************************************************** + * Implementation of digamma (psi), based on Cephes * + ****************************************************************************/ + +template <typename Scalar> +struct digamma_retval { + typedef Scalar type; +}; + +/* + * + * Polynomial evaluation helper for the Psi (digamma) function. + * + * digamma_impl_maybe_poly::run(s) evaluates the asymptotic Psi expansion for + * input Scalar s, assuming s is above 10.0. + * + * If s is above a certain threshold for the given Scalar type, zero + * is returned. Otherwise the polynomial is evaluated with enough + * coefficients for results matching Scalar machine precision. + * + * + */ +template <typename Scalar> +struct digamma_impl_maybe_poly { + EIGEN_DEVICE_FUNC + static EIGEN_STRONG_INLINE Scalar run(const Scalar) { + EIGEN_STATIC_ASSERT((internal::is_same<Scalar, Scalar>::value == false), + THIS_TYPE_IS_NOT_SUPPORTED); + return Scalar(0); + } +}; + + +template <> +struct digamma_impl_maybe_poly<float> { + EIGEN_DEVICE_FUNC + static EIGEN_STRONG_INLINE float run(const float s) { + const float A[] = { + -4.16666666666666666667E-3f, + 3.96825396825396825397E-3f, + -8.33333333333333333333E-3f, + 8.33333333333333333333E-2f + }; + + float z; + if (s < 1.0e8f) { + z = 1.0f / (s * s); + return z * cephes::polevl<float, 3>::run(z, A); + } else return 0.0f; + } +}; + +template <> +struct digamma_impl_maybe_poly<double> { + EIGEN_DEVICE_FUNC + static EIGEN_STRONG_INLINE double run(const double s) { + const double A[] = { + 8.33333333333333333333E-2, + -2.10927960927960927961E-2, + 7.57575757575757575758E-3, + -4.16666666666666666667E-3, + 3.96825396825396825397E-3, + -8.33333333333333333333E-3, + 8.33333333333333333333E-2 + }; + + double z; + if (s < 1.0e17) { + z = 1.0 / (s * s); + return z * cephes::polevl<double, 6>::run(z, A); + } + else return 0.0; + } +}; + +template <typename Scalar> +struct digamma_impl { + EIGEN_DEVICE_FUNC + static Scalar run(Scalar x) { + /* + * + * Psi (digamma) function (modified for Eigen) + * + * + * SYNOPSIS: + * + * double x, y, psi(); + * + * y = psi( x ); + * + * + * DESCRIPTION: + * + * d - + * psi(x) = -- ln | (x) + * dx + * + * is the logarithmic derivative of the gamma function. + * For integer x, + * n-1 + * - + * psi(n) = -EUL + > 1/k. + * - + * k=1 + * + * If x is negative, it is transformed to a positive argument by the + * reflection formula psi(1-x) = psi(x) + pi cot(pi x). + * For general positive x, the argument is made greater than 10 + * using the recurrence psi(x+1) = psi(x) + 1/x. + * Then the following asymptotic expansion is applied: + * + * inf. B + * - 2k + * psi(x) = log(x) - 1/2x - > ------- + * - 2k + * k=1 2k x + * + * where the B2k are Bernoulli numbers. + * + * ACCURACY (float): + * Relative error (except absolute when |psi| < 1): + * arithmetic domain # trials peak rms + * IEEE 0,30 30000 1.3e-15 1.4e-16 + * IEEE -30,0 40000 1.5e-15 2.2e-16 + * + * ACCURACY (double): + * Absolute error, relative when |psi| > 1 : + * arithmetic domain # trials peak rms + * IEEE -33,0 30000 8.2e-7 1.2e-7 + * IEEE 0,33 100000 7.3e-7 7.7e-8 + * + * ERROR MESSAGES: + * message condition value returned + * psi singularity x integer <=0 INFINITY + */ + + Scalar p, q, nz, s, w, y; + bool negative = false; + + const Scalar maxnum = NumTraits<Scalar>::infinity(); + const Scalar m_pi = Scalar(EIGEN_PI); + + const Scalar zero = Scalar(0); + const Scalar one = Scalar(1); + const Scalar half = Scalar(0.5); + nz = zero; + + if (x <= zero) { + negative = true; + q = x; + p = numext::floor(q); + if (p == q) { + return maxnum; + } + /* Remove the zeros of tan(m_pi x) + * by subtracting the nearest integer from x + */ + nz = q - p; + if (nz != half) { + if (nz > half) { + p += one; + nz = q - p; + } + nz = m_pi / numext::tan(m_pi * nz); + } + else { + nz = zero; + } + x = one - x; + } + + /* use the recurrence psi(x+1) = psi(x) + 1/x. */ + s = x; + w = zero; + while (s < Scalar(10)) { + w += one / s; + s += one; + } + + y = digamma_impl_maybe_poly<Scalar>::run(s); + + y = numext::log(s) - (half / s) - y - w; + + return (negative) ? y - nz : y; + } +}; + +/**************************************************************************** + * Implementation of erf, requires C++11/C99 * + ****************************************************************************/ + +template <typename Scalar> +struct erf_impl { + EIGEN_DEVICE_FUNC + static EIGEN_STRONG_INLINE Scalar run(const Scalar) { + EIGEN_STATIC_ASSERT((internal::is_same<Scalar, Scalar>::value == false), + THIS_TYPE_IS_NOT_SUPPORTED); + return Scalar(0); + } +}; + +template <typename Scalar> +struct erf_retval { + typedef Scalar type; +}; + +#if EIGEN_HAS_C99_MATH +template <> +struct erf_impl<float> { + EIGEN_DEVICE_FUNC + static EIGEN_STRONG_INLINE float run(float x) { return ::erff(x); } +}; + +template <> +struct erf_impl<double> { + EIGEN_DEVICE_FUNC + static EIGEN_STRONG_INLINE double run(double x) { return ::erf(x); } +}; +#endif // EIGEN_HAS_C99_MATH + +/*************************************************************************** +* Implementation of erfc, requires C++11/C99 * +****************************************************************************/ + +template <typename Scalar> +struct erfc_impl { + EIGEN_DEVICE_FUNC + static EIGEN_STRONG_INLINE Scalar run(const Scalar) { + EIGEN_STATIC_ASSERT((internal::is_same<Scalar, Scalar>::value == false), + THIS_TYPE_IS_NOT_SUPPORTED); + return Scalar(0); + } +}; + +template <typename Scalar> +struct erfc_retval { + typedef Scalar type; +}; + +#if EIGEN_HAS_C99_MATH +template <> +struct erfc_impl<float> { + EIGEN_DEVICE_FUNC + static EIGEN_STRONG_INLINE float run(const float x) { return ::erfcf(x); } +}; + +template <> +struct erfc_impl<double> { + EIGEN_DEVICE_FUNC + static EIGEN_STRONG_INLINE double run(const double x) { return ::erfc(x); } +}; +#endif // EIGEN_HAS_C99_MATH + +/************************************************************************************************************** + * Implementation of igammac (complemented incomplete gamma integral), based on Cephes but requires C++11/C99 * + **************************************************************************************************************/ + +template <typename Scalar> +struct igammac_retval { + typedef Scalar type; +}; + +// NOTE: cephes_helper is also used to implement zeta +template <typename Scalar> +struct cephes_helper { + EIGEN_DEVICE_FUNC + static EIGEN_STRONG_INLINE Scalar machep() { assert(false && "machep not supported for this type"); return 0.0; } + EIGEN_DEVICE_FUNC + static EIGEN_STRONG_INLINE Scalar big() { assert(false && "big not supported for this type"); return 0.0; } + EIGEN_DEVICE_FUNC + static EIGEN_STRONG_INLINE Scalar biginv() { assert(false && "biginv not supported for this type"); return 0.0; } +}; + +template <> +struct cephes_helper<float> { + EIGEN_DEVICE_FUNC + static EIGEN_STRONG_INLINE float machep() { + return NumTraits<float>::epsilon() / 2; // 1.0 - machep == 1.0 + } + EIGEN_DEVICE_FUNC + static EIGEN_STRONG_INLINE float big() { + // use epsneg (1.0 - epsneg == 1.0) + return 1.0f / (NumTraits<float>::epsilon() / 2); + } + EIGEN_DEVICE_FUNC + static EIGEN_STRONG_INLINE float biginv() { + // epsneg + return machep(); + } +}; + +template <> +struct cephes_helper<double> { + EIGEN_DEVICE_FUNC + static EIGEN_STRONG_INLINE double machep() { + return NumTraits<double>::epsilon() / 2; // 1.0 - machep == 1.0 + } + EIGEN_DEVICE_FUNC + static EIGEN_STRONG_INLINE double big() { + return 1.0 / NumTraits<double>::epsilon(); + } + EIGEN_DEVICE_FUNC + static EIGEN_STRONG_INLINE double biginv() { + // inverse of eps + return NumTraits<double>::epsilon(); + } +}; + +#if !EIGEN_HAS_C99_MATH + +template <typename Scalar> +struct igammac_impl { + EIGEN_DEVICE_FUNC + static Scalar run(Scalar a, Scalar x) { + EIGEN_STATIC_ASSERT((internal::is_same<Scalar, Scalar>::value == false), + THIS_TYPE_IS_NOT_SUPPORTED); + return Scalar(0); + } +}; + +#else + +template <typename Scalar> struct igamma_impl; // predeclare igamma_impl + +template <typename Scalar> +struct igammac_impl { + EIGEN_DEVICE_FUNC + static Scalar run(Scalar a, Scalar x) { + /* igamc() + * + * Incomplete gamma integral (modified for Eigen) + * + * + * + * SYNOPSIS: + * + * double a, x, y, igamc(); + * + * y = igamc( a, x ); + * + * DESCRIPTION: + * + * The function is defined by + * + * + * igamc(a,x) = 1 - igam(a,x) + * + * inf. + * - + * 1 | | -t a-1 + * = ----- | e t dt. + * - | | + * | (a) - + * x + * + * + * In this implementation both arguments must be positive. + * The integral is evaluated by either a power series or + * continued fraction expansion, depending on the relative + * values of a and x. + * + * ACCURACY (float): + * + * Relative error: + * arithmetic domain # trials peak rms + * IEEE 0,30 30000 7.8e-6 5.9e-7 + * + * + * ACCURACY (double): + * + * Tested at random a, x. + * a x Relative error: + * arithmetic domain domain # trials peak rms + * IEEE 0.5,100 0,100 200000 1.9e-14 1.7e-15 + * IEEE 0.01,0.5 0,100 200000 1.4e-13 1.6e-15 + * + */ + /* + Cephes Math Library Release 2.2: June, 1992 + Copyright 1985, 1987, 1992 by Stephen L. Moshier + Direct inquiries to 30 Frost Street, Cambridge, MA 02140 + */ + const Scalar zero = 0; + const Scalar one = 1; + const Scalar nan = NumTraits<Scalar>::quiet_NaN(); + + if ((x < zero) || (a <= zero)) { + // domain error + return nan; + } + + if ((x < one) || (x < a)) { + /* The checks above ensure that we meet the preconditions for + * igamma_impl::Impl(), so call it, rather than igamma_impl::Run(). + * Calling Run() would also work, but in that case the compiler may not be + * able to prove that igammac_impl::Run and igamma_impl::Run are not + * mutually recursive. This leads to worse code, particularly on + * platforms like nvptx, where recursion is allowed only begrudgingly. + */ + return (one - igamma_impl<Scalar>::Impl(a, x)); + } + + return Impl(a, x); + } + + private: + /* igamma_impl calls igammac_impl::Impl. */ + friend struct igamma_impl<Scalar>; + + /* Actually computes igamc(a, x). + * + * Preconditions: + * a > 0 + * x >= 1 + * x >= a + */ + EIGEN_DEVICE_FUNC static Scalar Impl(Scalar a, Scalar x) { + const Scalar zero = 0; + const Scalar one = 1; + const Scalar two = 2; + const Scalar machep = cephes_helper<Scalar>::machep(); + const Scalar maxlog = numext::log(NumTraits<Scalar>::highest()); + const Scalar big = cephes_helper<Scalar>::big(); + const Scalar biginv = cephes_helper<Scalar>::biginv(); + const Scalar inf = NumTraits<Scalar>::infinity(); + + Scalar ans, ax, c, yc, r, t, y, z; + Scalar pk, pkm1, pkm2, qk, qkm1, qkm2; + + if (x == inf) return zero; // std::isinf crashes on CUDA + + /* Compute x**a * exp(-x) / gamma(a) */ + ax = a * numext::log(x) - x - lgamma_impl<Scalar>::run(a); + if (ax < -maxlog) { // underflow + return zero; + } + ax = numext::exp(ax); + + // continued fraction + y = one - a; + z = x + y + one; + c = zero; + pkm2 = one; + qkm2 = x; + pkm1 = x + one; + qkm1 = z * x; + ans = pkm1 / qkm1; + + while (true) { + c += one; + y += one; + z += two; + yc = y * c; + pk = pkm1 * z - pkm2 * yc; + qk = qkm1 * z - qkm2 * yc; + if (qk != zero) { + r = pk / qk; + t = numext::abs((ans - r) / r); + ans = r; + } else { + t = one; + } + pkm2 = pkm1; + pkm1 = pk; + qkm2 = qkm1; + qkm1 = qk; + if (numext::abs(pk) > big) { + pkm2 *= biginv; + pkm1 *= biginv; + qkm2 *= biginv; + qkm1 *= biginv; + } + if (t <= machep) { + break; + } + } + + return (ans * ax); + } +}; + +#endif // EIGEN_HAS_C99_MATH + +/************************************************************************************************ + * Implementation of igamma (incomplete gamma integral), based on Cephes but requires C++11/C99 * + ************************************************************************************************/ + +template <typename Scalar> +struct igamma_retval { + typedef Scalar type; +}; + +#if !EIGEN_HAS_C99_MATH + +template <typename Scalar> +struct igamma_impl { + EIGEN_DEVICE_FUNC + static EIGEN_STRONG_INLINE Scalar run(Scalar a, Scalar x) { + EIGEN_STATIC_ASSERT((internal::is_same<Scalar, Scalar>::value == false), + THIS_TYPE_IS_NOT_SUPPORTED); + return Scalar(0); + } +}; + +#else + +template <typename Scalar> +struct igamma_impl { + EIGEN_DEVICE_FUNC + static Scalar run(Scalar a, Scalar x) { + /* igam() + * Incomplete gamma integral + * + * + * + * SYNOPSIS: + * + * double a, x, y, igam(); + * + * y = igam( a, x ); + * + * DESCRIPTION: + * + * The function is defined by + * + * x + * - + * 1 | | -t a-1 + * igam(a,x) = ----- | e t dt. + * - | | + * | (a) - + * 0 + * + * + * In this implementation both arguments must be positive. + * The integral is evaluated by either a power series or + * continued fraction expansion, depending on the relative + * values of a and x. + * + * ACCURACY (double): + * + * Relative error: + * arithmetic domain # trials peak rms + * IEEE 0,30 200000 3.6e-14 2.9e-15 + * IEEE 0,100 300000 9.9e-14 1.5e-14 + * + * + * ACCURACY (float): + * + * Relative error: + * arithmetic domain # trials peak rms + * IEEE 0,30 20000 7.8e-6 5.9e-7 + * + */ + /* + Cephes Math Library Release 2.2: June, 1992 + Copyright 1985, 1987, 1992 by Stephen L. Moshier + Direct inquiries to 30 Frost Street, Cambridge, MA 02140 + */ + + + /* left tail of incomplete gamma function: + * + * inf. k + * a -x - x + * x e > ---------- + * - - + * k=0 | (a+k+1) + * + */ + const Scalar zero = 0; + const Scalar one = 1; + const Scalar nan = NumTraits<Scalar>::quiet_NaN(); + + if (x == zero) return zero; + + if ((x < zero) || (a <= zero)) { // domain error + return nan; + } + + if ((x > one) && (x > a)) { + /* The checks above ensure that we meet the preconditions for + * igammac_impl::Impl(), so call it, rather than igammac_impl::Run(). + * Calling Run() would also work, but in that case the compiler may not be + * able to prove that igammac_impl::Run and igamma_impl::Run are not + * mutually recursive. This leads to worse code, particularly on + * platforms like nvptx, where recursion is allowed only begrudgingly. + */ + return (one - igammac_impl<Scalar>::Impl(a, x)); + } + + return Impl(a, x); + } + + private: + /* igammac_impl calls igamma_impl::Impl. */ + friend struct igammac_impl<Scalar>; + + /* Actually computes igam(a, x). + * + * Preconditions: + * x > 0 + * a > 0 + * !(x > 1 && x > a) + */ + EIGEN_DEVICE_FUNC static Scalar Impl(Scalar a, Scalar x) { + const Scalar zero = 0; + const Scalar one = 1; + const Scalar machep = cephes_helper<Scalar>::machep(); + const Scalar maxlog = numext::log(NumTraits<Scalar>::highest()); + + Scalar ans, ax, c, r; + + /* Compute x**a * exp(-x) / gamma(a) */ + ax = a * numext::log(x) - x - lgamma_impl<Scalar>::run(a); + if (ax < -maxlog) { + // underflow + return zero; + } + ax = numext::exp(ax); + + /* power series */ + r = a; + c = one; + ans = one; + + while (true) { + r += one; + c *= x/r; + ans += c; + if (c/ans <= machep) { + break; + } + } + + return (ans * ax / a); + } +}; + +#endif // EIGEN_HAS_C99_MATH + +/***************************************************************************** + * Implementation of Riemann zeta function of two arguments, based on Cephes * + *****************************************************************************/ + +template <typename Scalar> +struct zeta_retval { + typedef Scalar type; +}; + +template <typename Scalar> +struct zeta_impl_series { + EIGEN_DEVICE_FUNC + static EIGEN_STRONG_INLINE Scalar run(const Scalar) { + EIGEN_STATIC_ASSERT((internal::is_same<Scalar, Scalar>::value == false), + THIS_TYPE_IS_NOT_SUPPORTED); + return Scalar(0); + } +}; + +template <> +struct zeta_impl_series<float> { + EIGEN_DEVICE_FUNC + static EIGEN_STRONG_INLINE bool run(float& a, float& b, float& s, const float x, const float machep) { + int i = 0; + while(i < 9) + { + i += 1; + a += 1.0f; + b = numext::pow( a, -x ); + s += b; + if( numext::abs(b/s) < machep ) + return true; + } + + //Return whether we are done + return false; + } +}; + +template <> +struct zeta_impl_series<double> { + EIGEN_DEVICE_FUNC + static EIGEN_STRONG_INLINE bool run(double& a, double& b, double& s, const double x, const double machep) { + int i = 0; + while( (i < 9) || (a <= 9.0) ) + { + i += 1; + a += 1.0; + b = numext::pow( a, -x ); + s += b; + if( numext::abs(b/s) < machep ) + return true; + } + + //Return whether we are done + return false; + } +}; + +template <typename Scalar> +struct zeta_impl { + EIGEN_DEVICE_FUNC + static Scalar run(Scalar x, Scalar q) { + /* zeta.c + * + * Riemann zeta function of two arguments + * + * + * + * SYNOPSIS: + * + * double x, q, y, zeta(); + * + * y = zeta( x, q ); + * + * + * + * DESCRIPTION: + * + * + * + * inf. + * - -x + * zeta(x,q) = > (k+q) + * - + * k=0 + * + * where x > 1 and q is not a negative integer or zero. + * The Euler-Maclaurin summation formula is used to obtain + * the expansion + * + * n + * - -x + * zeta(x,q) = > (k+q) + * - + * k=1 + * + * 1-x inf. B x(x+1)...(x+2j) + * (n+q) 1 - 2j + * + --------- - ------- + > -------------------- + * x-1 x - x+2j+1 + * 2(n+q) j=1 (2j)! (n+q) + * + * where the B2j are Bernoulli numbers. Note that (see zetac.c) + * zeta(x,1) = zetac(x) + 1. + * + * + * + * ACCURACY: + * + * Relative error for single precision: + * arithmetic domain # trials peak rms + * IEEE 0,25 10000 6.9e-7 1.0e-7 + * + * Large arguments may produce underflow in powf(), in which + * case the results are inaccurate. + * + * REFERENCE: + * + * Gradshteyn, I. S., and I. M. Ryzhik, Tables of Integrals, + * Series, and Products, p. 1073; Academic Press, 1980. + * + */ + + int i; + Scalar p, r, a, b, k, s, t, w; + + const Scalar A[] = { + Scalar(12.0), + Scalar(-720.0), + Scalar(30240.0), + Scalar(-1209600.0), + Scalar(47900160.0), + Scalar(-1.8924375803183791606e9), /*1.307674368e12/691*/ + Scalar(7.47242496e10), + Scalar(-2.950130727918164224e12), /*1.067062284288e16/3617*/ + Scalar(1.1646782814350067249e14), /*5.109094217170944e18/43867*/ + Scalar(-4.5979787224074726105e15), /*8.028576626982912e20/174611*/ + Scalar(1.8152105401943546773e17), /*1.5511210043330985984e23/854513*/ + Scalar(-7.1661652561756670113e18) /*1.6938241367317436694528e27/236364091*/ + }; + + const Scalar maxnum = NumTraits<Scalar>::infinity(); + const Scalar zero = 0.0, half = 0.5, one = 1.0; + const Scalar machep = cephes_helper<Scalar>::machep(); + const Scalar nan = NumTraits<Scalar>::quiet_NaN(); + + if( x == one ) + return maxnum; + + if( x < one ) + { + return nan; + } + + if( q <= zero ) + { + if(q == numext::floor(q)) + { + return maxnum; + } + p = x; + r = numext::floor(p); + if (p != r) + return nan; + } + + /* Permit negative q but continue sum until n+q > +9 . + * This case should be handled by a reflection formula. + * If q<0 and x is an integer, there is a relation to + * the polygamma function. + */ + s = numext::pow( q, -x ); + a = q; + b = zero; + // Run the summation in a helper function that is specific to the floating precision + if (zeta_impl_series<Scalar>::run(a, b, s, x, machep)) { + return s; + } + + w = a; + s += b*w/(x-one); + s -= half * b; + a = one; + k = zero; + for( i=0; i<12; i++ ) + { + a *= x + k; + b /= w; + t = a*b/A[i]; + s = s + t; + t = numext::abs(t/s); + if( t < machep ) { + break; + } + k += one; + a *= x + k; + b /= w; + k += one; + } + return s; + } +}; + +/**************************************************************************** + * Implementation of polygamma function, requires C++11/C99 * + ****************************************************************************/ + +template <typename Scalar> +struct polygamma_retval { + typedef Scalar type; +}; + +#if !EIGEN_HAS_C99_MATH + +template <typename Scalar> +struct polygamma_impl { + EIGEN_DEVICE_FUNC + static EIGEN_STRONG_INLINE Scalar run(Scalar n, Scalar x) { + EIGEN_STATIC_ASSERT((internal::is_same<Scalar, Scalar>::value == false), + THIS_TYPE_IS_NOT_SUPPORTED); + return Scalar(0); + } +}; + +#else + +template <typename Scalar> +struct polygamma_impl { + EIGEN_DEVICE_FUNC + static Scalar run(Scalar n, Scalar x) { + Scalar zero = 0.0, one = 1.0; + Scalar nplus = n + one; + const Scalar nan = NumTraits<Scalar>::quiet_NaN(); + + // Check that n is an integer + if (numext::floor(n) != n) { + return nan; + } + // Just return the digamma function for n = 1 + else if (n == zero) { + return digamma_impl<Scalar>::run(x); + } + // Use the same implementation as scipy + else { + Scalar factorial = numext::exp(lgamma_impl<Scalar>::run(nplus)); + return numext::pow(-one, nplus) * factorial * zeta_impl<Scalar>::run(nplus, x); + } + } +}; + +#endif // EIGEN_HAS_C99_MATH + +/************************************************************************************************ + * Implementation of betainc (incomplete beta integral), based on Cephes but requires C++11/C99 * + ************************************************************************************************/ + +template <typename Scalar> +struct betainc_retval { + typedef Scalar type; +}; + +#if !EIGEN_HAS_C99_MATH + +template <typename Scalar> +struct betainc_impl { + EIGEN_DEVICE_FUNC + static EIGEN_STRONG_INLINE Scalar run(Scalar a, Scalar b, Scalar x) { + EIGEN_STATIC_ASSERT((internal::is_same<Scalar, Scalar>::value == false), + THIS_TYPE_IS_NOT_SUPPORTED); + return Scalar(0); + } +}; + +#else + +template <typename Scalar> +struct betainc_impl { + EIGEN_DEVICE_FUNC + static EIGEN_STRONG_INLINE Scalar run(Scalar, Scalar, Scalar) { + /* betaincf.c + * + * Incomplete beta integral + * + * + * SYNOPSIS: + * + * float a, b, x, y, betaincf(); + * + * y = betaincf( a, b, x ); + * + * + * DESCRIPTION: + * + * Returns incomplete beta integral of the arguments, evaluated + * from zero to x. The function is defined as + * + * x + * - - + * | (a+b) | | a-1 b-1 + * ----------- | t (1-t) dt. + * - - | | + * | (a) | (b) - + * 0 + * + * The domain of definition is 0 <= x <= 1. In this + * implementation a and b are restricted to positive values. + * The integral from x to 1 may be obtained by the symmetry + * relation + * + * 1 - betainc( a, b, x ) = betainc( b, a, 1-x ). + * + * The integral is evaluated by a continued fraction expansion. + * If a < 1, the function calls itself recursively after a + * transformation to increase a to a+1. + * + * ACCURACY (float): + * + * Tested at random points (a,b,x) with a and b in the indicated + * interval and x between 0 and 1. + * + * arithmetic domain # trials peak rms + * Relative error: + * IEEE 0,30 10000 3.7e-5 5.1e-6 + * IEEE 0,100 10000 1.7e-4 2.5e-5 + * The useful domain for relative error is limited by underflow + * of the single precision exponential function. + * Absolute error: + * IEEE 0,30 100000 2.2e-5 9.6e-7 + * IEEE 0,100 10000 6.5e-5 3.7e-6 + * + * Larger errors may occur for extreme ratios of a and b. + * + * ACCURACY (double): + * arithmetic domain # trials peak rms + * IEEE 0,5 10000 6.9e-15 4.5e-16 + * IEEE 0,85 250000 2.2e-13 1.7e-14 + * IEEE 0,1000 30000 5.3e-12 6.3e-13 + * IEEE 0,10000 250000 9.3e-11 7.1e-12 + * IEEE 0,100000 10000 8.7e-10 4.8e-11 + * Outputs smaller than the IEEE gradual underflow threshold + * were excluded from these statistics. + * + * ERROR MESSAGES: + * message condition value returned + * incbet domain x<0, x>1 nan + * incbet underflow nan + */ + + EIGEN_STATIC_ASSERT((internal::is_same<Scalar, Scalar>::value == false), + THIS_TYPE_IS_NOT_SUPPORTED); + return Scalar(0); + } +}; + +/* Continued fraction expansion #1 for incomplete beta integral (small_branch = True) + * Continued fraction expansion #2 for incomplete beta integral (small_branch = False) + */ +template <typename Scalar> +struct incbeta_cfe { + EIGEN_DEVICE_FUNC + static EIGEN_STRONG_INLINE Scalar run(Scalar a, Scalar b, Scalar x, bool small_branch) { + EIGEN_STATIC_ASSERT((internal::is_same<Scalar, float>::value || + internal::is_same<Scalar, double>::value), + THIS_TYPE_IS_NOT_SUPPORTED); + const Scalar big = cephes_helper<Scalar>::big(); + const Scalar machep = cephes_helper<Scalar>::machep(); + const Scalar biginv = cephes_helper<Scalar>::biginv(); + + const Scalar zero = 0; + const Scalar one = 1; + const Scalar two = 2; + + Scalar xk, pk, pkm1, pkm2, qk, qkm1, qkm2; + Scalar k1, k2, k3, k4, k5, k6, k7, k8, k26update; + Scalar ans; + int n; + + const int num_iters = (internal::is_same<Scalar, float>::value) ? 100 : 300; + const Scalar thresh = + (internal::is_same<Scalar, float>::value) ? machep : Scalar(3) * machep; + Scalar r = (internal::is_same<Scalar, float>::value) ? zero : one; + + if (small_branch) { + k1 = a; + k2 = a + b; + k3 = a; + k4 = a + one; + k5 = one; + k6 = b - one; + k7 = k4; + k8 = a + two; + k26update = one; + } else { + k1 = a; + k2 = b - one; + k3 = a; + k4 = a + one; + k5 = one; + k6 = a + b; + k7 = a + one; + k8 = a + two; + k26update = -one; + x = x / (one - x); + } + + pkm2 = zero; + qkm2 = one; + pkm1 = one; + qkm1 = one; + ans = one; + n = 0; + + do { + xk = -(x * k1 * k2) / (k3 * k4); + pk = pkm1 + pkm2 * xk; + qk = qkm1 + qkm2 * xk; + pkm2 = pkm1; + pkm1 = pk; + qkm2 = qkm1; + qkm1 = qk; + + xk = (x * k5 * k6) / (k7 * k8); + pk = pkm1 + pkm2 * xk; + qk = qkm1 + qkm2 * xk; + pkm2 = pkm1; + pkm1 = pk; + qkm2 = qkm1; + qkm1 = qk; + + if (qk != zero) { + r = pk / qk; + if (numext::abs(ans - r) < numext::abs(r) * thresh) { + return r; + } + ans = r; + } + + k1 += one; + k2 += k26update; + k3 += two; + k4 += two; + k5 += one; + k6 -= k26update; + k7 += two; + k8 += two; + + if ((numext::abs(qk) + numext::abs(pk)) > big) { + pkm2 *= biginv; + pkm1 *= biginv; + qkm2 *= biginv; + qkm1 *= biginv; + } + if ((numext::abs(qk) < biginv) || (numext::abs(pk) < biginv)) { + pkm2 *= big; + pkm1 *= big; + qkm2 *= big; + qkm1 *= big; + } + } while (++n < num_iters); + + return ans; + } +}; + +/* Helper functions depending on the Scalar type */ +template <typename Scalar> +struct betainc_helper {}; + +template <> +struct betainc_helper<float> { + /* Core implementation, assumes a large (> 1.0) */ + EIGEN_DEVICE_FUNC static EIGEN_STRONG_INLINE float incbsa(float aa, float bb, + float xx) { + float ans, a, b, t, x, onemx; + bool reversed_a_b = false; + + onemx = 1.0f - xx; + + /* see if x is greater than the mean */ + if (xx > (aa / (aa + bb))) { + reversed_a_b = true; + a = bb; + b = aa; + t = xx; + x = onemx; + } else { + a = aa; + b = bb; + t = onemx; + x = xx; + } + + /* Choose expansion for optimal convergence */ + if (b > 10.0f) { + if (numext::abs(b * x / a) < 0.3f) { + t = betainc_helper<float>::incbps(a, b, x); + if (reversed_a_b) t = 1.0f - t; + return t; + } + } + + ans = x * (a + b - 2.0f) / (a - 1.0f); + if (ans < 1.0f) { + ans = incbeta_cfe<float>::run(a, b, x, true /* small_branch */); + t = b * numext::log(t); + } else { + ans = incbeta_cfe<float>::run(a, b, x, false /* small_branch */); + t = (b - 1.0f) * numext::log(t); + } + + t += a * numext::log(x) + lgamma_impl<float>::run(a + b) - + lgamma_impl<float>::run(a) - lgamma_impl<float>::run(b); + t += numext::log(ans / a); + t = numext::exp(t); + + if (reversed_a_b) t = 1.0f - t; + return t; + } + + EIGEN_DEVICE_FUNC + static EIGEN_STRONG_INLINE float incbps(float a, float b, float x) { + float t, u, y, s; + const float machep = cephes_helper<float>::machep(); + + y = a * numext::log(x) + (b - 1.0f) * numext::log1p(-x) - numext::log(a); + y -= lgamma_impl<float>::run(a) + lgamma_impl<float>::run(b); + y += lgamma_impl<float>::run(a + b); + + t = x / (1.0f - x); + s = 0.0f; + u = 1.0f; + do { + b -= 1.0f; + if (b == 0.0f) { + break; + } + a += 1.0f; + u *= t * b / a; + s += u; + } while (numext::abs(u) > machep); + + return numext::exp(y) * (1.0f + s); + } +}; + +template <> +struct betainc_impl<float> { + EIGEN_DEVICE_FUNC + static float run(float a, float b, float x) { + const float nan = NumTraits<float>::quiet_NaN(); + float ans, t; + + if (a <= 0.0f) return nan; + if (b <= 0.0f) return nan; + if ((x <= 0.0f) || (x >= 1.0f)) { + if (x == 0.0f) return 0.0f; + if (x == 1.0f) return 1.0f; + // mtherr("betaincf", DOMAIN); + return nan; + } + + /* transformation for small aa */ + if (a <= 1.0f) { + ans = betainc_helper<float>::incbsa(a + 1.0f, b, x); + t = a * numext::log(x) + b * numext::log1p(-x) + + lgamma_impl<float>::run(a + b) - lgamma_impl<float>::run(a + 1.0f) - + lgamma_impl<float>::run(b); + return (ans + numext::exp(t)); + } else { + return betainc_helper<float>::incbsa(a, b, x); + } + } +}; + +template <> +struct betainc_helper<double> { + EIGEN_DEVICE_FUNC + static EIGEN_STRONG_INLINE double incbps(double a, double b, double x) { + const double machep = cephes_helper<double>::machep(); + + double s, t, u, v, n, t1, z, ai; + + ai = 1.0 / a; + u = (1.0 - b) * x; + v = u / (a + 1.0); + t1 = v; + t = u; + n = 2.0; + s = 0.0; + z = machep * ai; + while (numext::abs(v) > z) { + u = (n - b) * x / n; + t *= u; + v = t / (a + n); + s += v; + n += 1.0; + } + s += t1; + s += ai; + + u = a * numext::log(x); + // TODO: gamma() is not directly implemented in Eigen. + /* + if ((a + b) < maxgam && numext::abs(u) < maxlog) { + t = gamma(a + b) / (gamma(a) * gamma(b)); + s = s * t * pow(x, a); + } else { + */ + t = lgamma_impl<double>::run(a + b) - lgamma_impl<double>::run(a) - + lgamma_impl<double>::run(b) + u + numext::log(s); + return s = numext::exp(t); + } +}; + +template <> +struct betainc_impl<double> { + EIGEN_DEVICE_FUNC + static double run(double aa, double bb, double xx) { + const double nan = NumTraits<double>::quiet_NaN(); + const double machep = cephes_helper<double>::machep(); + // const double maxgam = 171.624376956302725; + + double a, b, t, x, xc, w, y; + bool reversed_a_b = false; + + if (aa <= 0.0 || bb <= 0.0) { + return nan; // goto domerr; + } + + if ((xx <= 0.0) || (xx >= 1.0)) { + if (xx == 0.0) return (0.0); + if (xx == 1.0) return (1.0); + // mtherr("incbet", DOMAIN); + return nan; + } + + if ((bb * xx) <= 1.0 && xx <= 0.95) { + return betainc_helper<double>::incbps(aa, bb, xx); + } + + w = 1.0 - xx; + + /* Reverse a and b if x is greater than the mean. */ + if (xx > (aa / (aa + bb))) { + reversed_a_b = true; + a = bb; + b = aa; + xc = xx; + x = w; + } else { + a = aa; + b = bb; + xc = w; + x = xx; + } + + if (reversed_a_b && (b * x) <= 1.0 && x <= 0.95) { + t = betainc_helper<double>::incbps(a, b, x); + if (t <= machep) { + t = 1.0 - machep; + } else { + t = 1.0 - t; + } + return t; + } + + /* Choose expansion for better convergence. */ + y = x * (a + b - 2.0) - (a - 1.0); + if (y < 0.0) { + w = incbeta_cfe<double>::run(a, b, x, true /* small_branch */); + } else { + w = incbeta_cfe<double>::run(a, b, x, false /* small_branch */) / xc; + } + + /* Multiply w by the factor + a b _ _ _ + x (1-x) | (a+b) / ( a | (a) | (b) ) . */ + + y = a * numext::log(x); + t = b * numext::log(xc); + // TODO: gamma is not directly implemented in Eigen. + /* + if ((a + b) < maxgam && numext::abs(y) < maxlog && numext::abs(t) < maxlog) + { + t = pow(xc, b); + t *= pow(x, a); + t /= a; + t *= w; + t *= gamma(a + b) / (gamma(a) * gamma(b)); + } else { + */ + /* Resort to logarithms. */ + y += t + lgamma_impl<double>::run(a + b) - lgamma_impl<double>::run(a) - + lgamma_impl<double>::run(b); + y += numext::log(w / a); + t = numext::exp(y); + + /* } */ + // done: + + if (reversed_a_b) { + if (t <= machep) { + t = 1.0 - machep; + } else { + t = 1.0 - t; + } + } + return t; + } +}; + +#endif // EIGEN_HAS_C99_MATH + +} // end namespace internal + +namespace numext { + +template <typename Scalar> +EIGEN_DEVICE_FUNC inline EIGEN_MATHFUNC_RETVAL(lgamma, Scalar) + lgamma(const Scalar& x) { + return EIGEN_MATHFUNC_IMPL(lgamma, Scalar)::run(x); +} + +template <typename Scalar> +EIGEN_DEVICE_FUNC inline EIGEN_MATHFUNC_RETVAL(digamma, Scalar) + digamma(const Scalar& x) { + return EIGEN_MATHFUNC_IMPL(digamma, Scalar)::run(x); +} + +template <typename Scalar> +EIGEN_DEVICE_FUNC inline EIGEN_MATHFUNC_RETVAL(zeta, Scalar) +zeta(const Scalar& x, const Scalar& q) { + return EIGEN_MATHFUNC_IMPL(zeta, Scalar)::run(x, q); +} + +template <typename Scalar> +EIGEN_DEVICE_FUNC inline EIGEN_MATHFUNC_RETVAL(polygamma, Scalar) +polygamma(const Scalar& n, const Scalar& x) { + return EIGEN_MATHFUNC_IMPL(polygamma, Scalar)::run(n, x); +} + +template <typename Scalar> +EIGEN_DEVICE_FUNC inline EIGEN_MATHFUNC_RETVAL(erf, Scalar) + erf(const Scalar& x) { + return EIGEN_MATHFUNC_IMPL(erf, Scalar)::run(x); +} + +template <typename Scalar> +EIGEN_DEVICE_FUNC inline EIGEN_MATHFUNC_RETVAL(erfc, Scalar) + erfc(const Scalar& x) { + return EIGEN_MATHFUNC_IMPL(erfc, Scalar)::run(x); +} + +template <typename Scalar> +EIGEN_DEVICE_FUNC inline EIGEN_MATHFUNC_RETVAL(igamma, Scalar) + igamma(const Scalar& a, const Scalar& x) { + return EIGEN_MATHFUNC_IMPL(igamma, Scalar)::run(a, x); +} + +template <typename Scalar> +EIGEN_DEVICE_FUNC inline EIGEN_MATHFUNC_RETVAL(igammac, Scalar) + igammac(const Scalar& a, const Scalar& x) { + return EIGEN_MATHFUNC_IMPL(igammac, Scalar)::run(a, x); +} + +template <typename Scalar> +EIGEN_DEVICE_FUNC inline EIGEN_MATHFUNC_RETVAL(betainc, Scalar) + betainc(const Scalar& a, const Scalar& b, const Scalar& x) { + return EIGEN_MATHFUNC_IMPL(betainc, Scalar)::run(a, b, x); +} + +} // end namespace numext + + +} // end namespace Eigen + +#endif // EIGEN_SPECIAL_FUNCTIONS_H |