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Diffstat (limited to 'Eigen/src/Core/SpecialFunctions.h')
| -rw-r--r-- | Eigen/src/Core/SpecialFunctions.h | 274 |
1 files changed, 274 insertions, 0 deletions
diff --git a/Eigen/src/Core/SpecialFunctions.h b/Eigen/src/Core/SpecialFunctions.h index 37ebb5915..2a0a6ff15 100644 --- a/Eigen/src/Core/SpecialFunctions.h +++ b/Eigen/src/Core/SpecialFunctions.h @@ -722,6 +722,268 @@ struct igamma_impl { #endif // EIGEN_HAS_C99_MATH +/**************************************************************************** + * Implementation of Riemann zeta function of two arguments * + ****************************************************************************/ + +template <typename Scalar> +struct zeta_retval { + typedef Scalar type; +}; + +#ifndef EIGEN_HAS_C99_MATH + +template <typename Scalar> +struct zeta_impl { + EIGEN_DEVICE_FUNC + static Scalar run(Scalar x, Scalar q) { + EIGEN_STATIC_ASSERT((internal::is_same<Scalar, Scalar>::value == false), + THIS_TYPE_IS_NOT_SUPPORTED); + return Scalar(0); + } +}; + +#else + +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 EIGEN_STRONG_INLINE + static 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 EIGEN_STRONG_INLINE + static 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 = igamma_helper<Scalar>::machep(); + + if( x == one ) + return maxnum; + + if( x < one ) + { + return zero; + } + + if( q <= zero ) + { + if(q == numext::floor(q)) + { + return maxnum; + } + p = x; + r = numext::floor(p); + if (p != r) + return zero; + } + + /* 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 ) + return s; + k += one; + a *= x + k; + b /= w; + k += one; + } + return s; + } +}; + +#endif // EIGEN_HAS_C99_MATH + +/**************************************************************************** + * Implementation of polygamma function * + ****************************************************************************/ + +template <typename Scalar> +struct polygamma_retval { + typedef Scalar type; +}; + +#ifndef EIGEN_HAS_C99_MATH + +template <typename Scalar> +struct polygamma_impl { + EIGEN_DEVICE_FUNC + static 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; + + // Just return the digamma function for n = 1 + 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 + } // end namespace internal namespace numext { @@ -737,6 +999,18 @@ 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) |