EllipticFunction.hpp
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/**
* \file EllipticFunction.hpp
* \brief Header for GeographicLib::EllipticFunction class
*
* Copyright (c) Charles Karney (2008-2022) <karney@alum.mit.edu> and licensed
* under the MIT/X11 License. For more information, see
* https://geographiclib.sourceforge.io/
**********************************************************************/
#if !defined(GEOGRAPHICLIB_ELLIPTICFUNCTION_HPP)
#define GEOGRAPHICLIB_ELLIPTICFUNCTION_HPP 1
#include <GeographicLib/Constants.hpp>
namespace GeographicLib {
/**
* \brief Elliptic integrals and functions
*
* This provides the elliptic functions and integrals needed for Ellipsoid,
* GeodesicExact, and TransverseMercatorExact. Two categories of function
* are provided:
* - \e static functions to compute symmetric elliptic integrals
* (https://dlmf.nist.gov/19.16.i)
* - \e member functions to compute Legrendre's elliptic
* integrals (https://dlmf.nist.gov/19.2.ii) and the
* Jacobi elliptic functions (https://dlmf.nist.gov/22.2).
* .
* In the latter case, an object is constructed giving the modulus \e k (and
* optionally the parameter &alpha;<sup>2</sup>). The modulus is always
* passed as its square <i>k</i><sup>2</sup> which allows \e k to be pure
* imaginary (<i>k</i><sup>2</sup> &lt; 0). (Confusingly, Abramowitz and
* Stegun call \e m = <i>k</i><sup>2</sup> the "parameter" and \e n =
* &alpha;<sup>2</sup> the "characteristic".)
*
* In geodesic applications, it is convenient to separate the incomplete
* integrals into secular and periodic components, e.g.,
* \f[
* E(\phi, k) = (2 E(k) / \pi) [ \phi + \delta E(\phi, k) ]
* \f]
* where &delta;\e E(&phi;, \e k) is an odd periodic function with period
* &pi;.
*
* The computation of the elliptic integrals uses the algorithms given in
* - B. C. Carlson,
* <a href="https://doi.org/10.1007/BF02198293"> Computation of real or
* complex elliptic integrals</a>, Numerical Algorithms 10, 13--26 (1995);
* <a href="https://arxiv.org/abs/math/9409227">preprint</a>.
* .
* with the additional optimizations given in https://dlmf.nist.gov/19.36.i.
* The computation of the Jacobi elliptic functions uses the algorithm given
* in
* - R. Bulirsch,
* <a href="https://doi.org/10.1007/BF01397975"> Numerical Calculation of
* Elliptic Integrals and Elliptic Functions</a>, Numericshe Mathematik 7,
* 78--90 (1965).
* .
* The notation follows https://dlmf.nist.gov/19 and https://dlmf.nist.gov/22
*
* Example of use:
* \include example-EllipticFunction.cpp
**********************************************************************/
class GEOGRAPHICLIB_EXPORT EllipticFunction {
private:
typedef Math::real real;
enum { num_ = 13 }; // Max depth required for sncndn; probably 5 is enough.
real _k2, _kp2, _alpha2, _alphap2, _eps;
real _kKc, _eEc, _dDc, _pPic, _gGc, _hHc;
public:
/** \name Constructor
**********************************************************************/
///@{
/**
* Constructor specifying the modulus and parameter.
*
* @param[in] k2 the square of the modulus <i>k</i><sup>2</sup>.
* <i>k</i><sup>2</sup> must lie in (&minus;&infin;, 1].
* @param[in] alpha2 the parameter &alpha;<sup>2</sup>.
* &alpha;<sup>2</sup> must lie in (&minus;&infin;, 1].
* @exception GeographicErr if \e k2 or \e alpha2 is out of its legal
* range.
*
* If only elliptic integrals of the first and second kinds are needed,
* then set &alpha;<sup>2</sup> = 0 (the default value); in this case, we
* have &Pi;(&phi;, 0, \e k) = \e F(&phi;, \e k), \e G(&phi;, 0, \e k) = \e
* E(&phi;, \e k), and \e H(&phi;, 0, \e k) = \e F(&phi;, \e k) - \e
* D(&phi;, \e k).
**********************************************************************/
EllipticFunction(real k2 = 0, real alpha2 = 0)
{ Reset(k2, alpha2); }
/**
* Constructor specifying the modulus and parameter and their complements.
*
* @param[in] k2 the square of the modulus <i>k</i><sup>2</sup>.
* <i>k</i><sup>2</sup> must lie in (&minus;&infin;, 1].
* @param[in] alpha2 the parameter &alpha;<sup>2</sup>.
* &alpha;<sup>2</sup> must lie in (&minus;&infin;, 1].
* @param[in] kp2 the complementary modulus squared <i>k'</i><sup>2</sup> =
* 1 &minus; <i>k</i><sup>2</sup>. This must lie in [0, &infin;).
* @param[in] alphap2 the complementary parameter &alpha;'<sup>2</sup> = 1
* &minus; &alpha;<sup>2</sup>. This must lie in [0, &infin;).
* @exception GeographicErr if \e k2, \e alpha2, \e kp2, or \e alphap2 is
* out of its legal range.
*
* The arguments must satisfy \e k2 + \e kp2 = 1 and \e alpha2 + \e alphap2
* = 1. (No checking is done that these conditions are met.) This
* constructor is provided to enable accuracy to be maintained, e.g., when
* \e k is very close to unity.
**********************************************************************/
EllipticFunction(real k2, real alpha2, real kp2, real alphap2)
{ Reset(k2, alpha2, kp2, alphap2); }
/**
* Reset the modulus and parameter.
*
* @param[in] k2 the new value of square of the modulus
* <i>k</i><sup>2</sup> which must lie in (&minus;&infin;, ].
* done.)
* @param[in] alpha2 the new value of parameter &alpha;<sup>2</sup>.
* &alpha;<sup>2</sup> must lie in (&minus;&infin;, 1].
* @exception GeographicErr if \e k2 or \e alpha2 is out of its legal
* range.
**********************************************************************/
void Reset(real k2 = 0, real alpha2 = 0)
{ Reset(k2, alpha2, 1 - k2, 1 - alpha2); }
/**
* Reset the modulus and parameter supplying also their complements.
*
* @param[in] k2 the square of the modulus <i>k</i><sup>2</sup>.
* <i>k</i><sup>2</sup> must lie in (&minus;&infin;, 1].
* @param[in] alpha2 the parameter &alpha;<sup>2</sup>.
* &alpha;<sup>2</sup> must lie in (&minus;&infin;, 1].
* @param[in] kp2 the complementary modulus squared <i>k'</i><sup>2</sup> =
* 1 &minus; <i>k</i><sup>2</sup>. This must lie in [0, &infin;).
* @param[in] alphap2 the complementary parameter &alpha;'<sup>2</sup> = 1
* &minus; &alpha;<sup>2</sup>. This must lie in [0, &infin;).
* @exception GeographicErr if \e k2, \e alpha2, \e kp2, or \e alphap2 is
* out of its legal range.
*
* The arguments must satisfy \e k2 + \e kp2 = 1 and \e alpha2 + \e alphap2
* = 1. (No checking is done that these conditions are met.) This
* constructor is provided to enable accuracy to be maintained, e.g., when
* is very small.
**********************************************************************/
void Reset(real k2, real alpha2, real kp2, real alphap2);
///@}
/** \name Inspector functions.
**********************************************************************/
///@{
/**
* @return the square of the modulus <i>k</i><sup>2</sup>.
**********************************************************************/
Math::real k2() const { return _k2; }
/**
* @return the square of the complementary modulus <i>k'</i><sup>2</sup> =
* 1 &minus; <i>k</i><sup>2</sup>.
**********************************************************************/
Math::real kp2() const { return _kp2; }
/**
* @return the parameter &alpha;<sup>2</sup>.
**********************************************************************/
Math::real alpha2() const { return _alpha2; }
/**
* @return the complementary parameter &alpha;'<sup>2</sup> = 1 &minus;
* &alpha;<sup>2</sup>.
**********************************************************************/
Math::real alphap2() const { return _alphap2; }
///@}
/** \name Complete elliptic integrals.
**********************************************************************/
///@{
/**
* The complete integral of the first kind.
*
* @return \e K(\e k).
*
* \e K(\e k) is defined in https://dlmf.nist.gov/19.2.E4
* \f[
* K(k) = \int_0^{\pi/2} \frac1{\sqrt{1-k^2\sin^2\phi}}\,d\phi.
* \f]
**********************************************************************/
Math::real K() const { return _kKc; }
/**
* The complete integral of the second kind.
*
* @return \e E(\e k).
*
* \e E(\e k) is defined in https://dlmf.nist.gov/19.2.E5
* \f[
* E(k) = \int_0^{\pi/2} \sqrt{1-k^2\sin^2\phi}\,d\phi.
* \f]
**********************************************************************/
Math::real E() const { return _eEc; }
/**
* Jahnke's complete integral.
*
* @return \e D(\e k).
*
* \e D(\e k) is defined in https://dlmf.nist.gov/19.2.E6
* \f[
* D(k) =
* \int_0^{\pi/2} \frac{\sin^2\phi}{\sqrt{1-k^2\sin^2\phi}}\,d\phi.
* \f]
**********************************************************************/
Math::real D() const { return _dDc; }
/**
* The difference between the complete integrals of the first and second
* kinds.
*
* @return \e K(\e k) &minus; \e E(\e k).
**********************************************************************/
Math::real KE() const { return _k2 * _dDc; }
/**
* The complete integral of the third kind.
*
* @return &Pi;(&alpha;<sup>2</sup>, \e k).
*
* &Pi;(&alpha;<sup>2</sup>, \e k) is defined in
* https://dlmf.nist.gov/19.2.E7
* \f[
* \Pi(\alpha^2, k) = \int_0^{\pi/2}
* \frac1{\sqrt{1-k^2\sin^2\phi}(1 - \alpha^2\sin^2\phi)}\,d\phi.
* \f]
**********************************************************************/
Math::real Pi() const { return _pPic; }
/**
* Legendre's complete geodesic longitude integral.
*
* @return \e G(&alpha;<sup>2</sup>, \e k).
*
* \e G(&alpha;<sup>2</sup>, \e k) is given by
* \f[
* G(\alpha^2, k) = \int_0^{\pi/2}
* \frac{\sqrt{1-k^2\sin^2\phi}}{1 - \alpha^2\sin^2\phi}\,d\phi.
* \f]
**********************************************************************/
Math::real G() const { return _gGc; }
/**
* Cayley's complete geodesic longitude difference integral.
*
* @return \e H(&alpha;<sup>2</sup>, \e k).
*
* \e H(&alpha;<sup>2</sup>, \e k) is given by
* \f[
* H(\alpha^2, k) = \int_0^{\pi/2}
* \frac{\cos^2\phi}{(1-\alpha^2\sin^2\phi)\sqrt{1-k^2\sin^2\phi}}
* \,d\phi.
* \f]
**********************************************************************/
Math::real H() const { return _hHc; }
///@}
/** \name Incomplete elliptic integrals.
**********************************************************************/
///@{
/**
* The incomplete integral of the first kind.
*
* @param[in] phi
* @return \e F(&phi;, \e k).
*
* \e F(&phi;, \e k) is defined in https://dlmf.nist.gov/19.2.E4
* \f[
* F(\phi, k) = \int_0^\phi \frac1{\sqrt{1-k^2\sin^2\theta}}\,d\theta.
* \f]
**********************************************************************/
Math::real F(real phi) const;
/**
* The incomplete integral of the second kind.
*
* @param[in] phi
* @return \e E(&phi;, \e k).
*
* \e E(&phi;, \e k) is defined in https://dlmf.nist.gov/19.2.E5
* \f[
* E(\phi, k) = \int_0^\phi \sqrt{1-k^2\sin^2\theta}\,d\theta.
* \f]
**********************************************************************/
Math::real E(real phi) const;
/**
* The incomplete integral of the second kind with the argument given in
* degrees.
*
* @param[in] ang in <i>degrees</i>.
* @return \e E(&pi; <i>ang</i>/180, \e k).
**********************************************************************/
Math::real Ed(real ang) const;
/**
* The inverse of the incomplete integral of the second kind.
*
* @param[in] x
* @return &phi; = <i>E</i><sup>&minus;1</sup>(\e x, \e k); i.e., the
* solution of such that \e E(&phi;, \e k) = \e x.
**********************************************************************/
Math::real Einv(real x) const;
/**
* The incomplete integral of the third kind.
*
* @param[in] phi
* @return &Pi;(&phi;, &alpha;<sup>2</sup>, \e k).
*
* &Pi;(&phi;, &alpha;<sup>2</sup>, \e k) is defined in
* https://dlmf.nist.gov/19.2.E7
* \f[
* \Pi(\phi, \alpha^2, k) = \int_0^\phi
* \frac1{\sqrt{1-k^2\sin^2\theta}(1 - \alpha^2\sin^2\theta)}\,d\theta.
* \f]
**********************************************************************/
Math::real Pi(real phi) const;
/**
* Jahnke's incomplete elliptic integral.
*
* @param[in] phi
* @return \e D(&phi;, \e k).
*
* \e D(&phi;, \e k) is defined in https://dlmf.nist.gov/19.2.E4
* \f[
* D(\phi, k) = \int_0^\phi
* \frac{\sin^2\theta}{\sqrt{1-k^2\sin^2\theta}}\,d\theta.
* \f]
**********************************************************************/
Math::real D(real phi) const;
/**
* Legendre's geodesic longitude integral.
*
* @param[in] phi
* @return \e G(&phi;, &alpha;<sup>2</sup>, \e k).
*
* \e G(&phi;, &alpha;<sup>2</sup>, \e k) is defined by
* \f[
* \begin{align}
* G(\phi, \alpha^2, k) &=
* \frac{k^2}{\alpha^2} F(\phi, k) +
* \biggl(1 - \frac{k^2}{\alpha^2}\biggr) \Pi(\phi, \alpha^2, k) \\
* &= \int_0^\phi
* \frac{\sqrt{1-k^2\sin^2\theta}}{1 - \alpha^2\sin^2\theta}\,d\theta.
* \end{align}
* \f]
*
* Legendre expresses the longitude of a point on the geodesic in terms of
* this combination of elliptic integrals in Exercices de Calcul
* Int&eacute;gral, Vol. 1 (1811), p. 181,
* https://books.google.com/books?id=riIOAAAAQAAJ&pg=PA181.
*
* See \ref geodellip for the expression for the longitude in terms of this
* function.
**********************************************************************/
Math::real G(real phi) const;
/**
* Cayley's geodesic longitude difference integral.
*
* @param[in] phi
* @return \e H(&phi;, &alpha;<sup>2</sup>, \e k).
*
* \e H(&phi;, &alpha;<sup>2</sup>, \e k) is defined by
* \f[
* \begin{align}
* H(\phi, \alpha^2, k) &=
* \frac1{\alpha^2} F(\phi, k) +
* \biggl(1 - \frac1{\alpha^2}\biggr) \Pi(\phi, \alpha^2, k) \\
* &= \int_0^\phi
* \frac{\cos^2\theta}
* {(1-\alpha^2\sin^2\theta)\sqrt{1-k^2\sin^2\theta}}
* \,d\theta.
* \end{align}
* \f]
*
* Cayley expresses the longitude difference of a point on the geodesic in
* terms of this combination of elliptic integrals in Phil. Mag. <b>40</b>
* (1870), p. 333, https://books.google.com/books?id=Zk0wAAAAIAAJ&pg=PA333.
*
* See \ref geodellip for the expression for the longitude in terms of this
* function.
**********************************************************************/
Math::real H(real phi) const;
///@}
/** \name Incomplete integrals in terms of Jacobi elliptic functions.
**********************************************************************/
///@{
/**
* The incomplete integral of the first kind in terms of Jacobi elliptic
* functions.
*
* @param[in] sn = sin&phi;.
* @param[in] cn = cos&phi;.
* @param[in] dn = sqrt(1 &minus; <i>k</i><sup>2</sup>
* sin<sup>2</sup>&phi;).
* @return \e F(&phi;, \e k) as though &phi; &isin; (&minus;&pi;, &pi;].
**********************************************************************/
Math::real F(real sn, real cn, real dn) const;
/**
* The incomplete integral of the second kind in terms of Jacobi elliptic
* functions.
*
* @param[in] sn = sin&phi;.
* @param[in] cn = cos&phi;.
* @param[in] dn = sqrt(1 &minus; <i>k</i><sup>2</sup>
* sin<sup>2</sup>&phi;).
* @return \e E(&phi;, \e k) as though &phi; &isin; (&minus;&pi;, &pi;].
**********************************************************************/
Math::real E(real sn, real cn, real dn) const;
/**
* The incomplete integral of the third kind in terms of Jacobi elliptic
* functions.
*
* @param[in] sn = sin&phi;.
* @param[in] cn = cos&phi;.
* @param[in] dn = sqrt(1 &minus; <i>k</i><sup>2</sup>
* sin<sup>2</sup>&phi;).
* @return &Pi;(&phi;, &alpha;<sup>2</sup>, \e k) as though &phi; &isin;
* (&minus;&pi;, &pi;].
**********************************************************************/
Math::real Pi(real sn, real cn, real dn) const;
/**
* Jahnke's incomplete elliptic integral in terms of Jacobi elliptic
* functions.
*
* @param[in] sn = sin&phi;.
* @param[in] cn = cos&phi;.
* @param[in] dn = sqrt(1 &minus; <i>k</i><sup>2</sup>
* sin<sup>2</sup>&phi;).
* @return \e D(&phi;, \e k) as though &phi; &isin; (&minus;&pi;, &pi;].
**********************************************************************/
Math::real D(real sn, real cn, real dn) const;
/**
* Legendre's geodesic longitude integral in terms of Jacobi elliptic
* functions.
*
* @param[in] sn = sin&phi;.
* @param[in] cn = cos&phi;.
* @param[in] dn = sqrt(1 &minus; <i>k</i><sup>2</sup>
* sin<sup>2</sup>&phi;).
* @return \e G(&phi;, &alpha;<sup>2</sup>, \e k) as though &phi; &isin;
* (&minus;&pi;, &pi;].
**********************************************************************/
Math::real G(real sn, real cn, real dn) const;
/**
* Cayley's geodesic longitude difference integral in terms of Jacobi
* elliptic functions.
*
* @param[in] sn = sin&phi;.
* @param[in] cn = cos&phi;.
* @param[in] dn = sqrt(1 &minus; <i>k</i><sup>2</sup>
* sin<sup>2</sup>&phi;).
* @return \e H(&phi;, &alpha;<sup>2</sup>, \e k) as though &phi; &isin;
* (&minus;&pi;, &pi;].
**********************************************************************/
Math::real H(real sn, real cn, real dn) const;
///@}
/** \name Periodic versions of incomplete elliptic integrals.
**********************************************************************/
///@{
/**
* The periodic incomplete integral of the first kind.
*
* @param[in] sn = sin&phi;.
* @param[in] cn = cos&phi;.
* @param[in] dn = sqrt(1 &minus; <i>k</i><sup>2</sup>
* sin<sup>2</sup>&phi;).
* @return the periodic function &pi; \e F(&phi;, \e k) / (2 \e K(\e k)) -
* &phi;.
**********************************************************************/
Math::real deltaF(real sn, real cn, real dn) const;
/**
* The periodic incomplete integral of the second kind.
*
* @param[in] sn = sin&phi;.
* @param[in] cn = cos&phi;.
* @param[in] dn = sqrt(1 &minus; <i>k</i><sup>2</sup>
* sin<sup>2</sup>&phi;).
* @return the periodic function &pi; \e E(&phi;, \e k) / (2 \e E(\e k)) -
* &phi;.
**********************************************************************/
Math::real deltaE(real sn, real cn, real dn) const;
/**
* The periodic inverse of the incomplete integral of the second kind.
*
* @param[in] stau = sin&tau;.
* @param[in] ctau = sin&tau;.
* @return the periodic function <i>E</i><sup>&minus;1</sup>(&tau; (2 \e
* E(\e k)/&pi;), \e k) - &tau;.
**********************************************************************/
Math::real deltaEinv(real stau, real ctau) const;
/**
* The periodic incomplete integral of the third kind.
*
* @param[in] sn = sin&phi;.
* @param[in] cn = cos&phi;.
* @param[in] dn = sqrt(1 &minus; <i>k</i><sup>2</sup>
* sin<sup>2</sup>&phi;).
* @return the periodic function &pi; &Pi;(&phi;, &alpha;<sup>2</sup>,
* \e k) / (2 &Pi;(&alpha;<sup>2</sup>, \e k)) - &phi;.
**********************************************************************/
Math::real deltaPi(real sn, real cn, real dn) const;
/**
* The periodic Jahnke's incomplete elliptic integral.
*
* @param[in] sn = sin&phi;.
* @param[in] cn = cos&phi;.
* @param[in] dn = sqrt(1 &minus; <i>k</i><sup>2</sup>
* sin<sup>2</sup>&phi;).
* @return the periodic function &pi; \e D(&phi;, \e k) / (2 \e D(\e k)) -
* &phi;.
**********************************************************************/
Math::real deltaD(real sn, real cn, real dn) const;
/**
* Legendre's periodic geodesic longitude integral.
*
* @param[in] sn = sin&phi;.
* @param[in] cn = cos&phi;.
* @param[in] dn = sqrt(1 &minus; <i>k</i><sup>2</sup>
* sin<sup>2</sup>&phi;).
* @return the periodic function &pi; \e G(&phi;, \e k) / (2 \e G(\e k)) -
* &phi;.
**********************************************************************/
Math::real deltaG(real sn, real cn, real dn) const;
/**
* Cayley's periodic geodesic longitude difference integral.
*
* @param[in] sn = sin&phi;.
* @param[in] cn = cos&phi;.
* @param[in] dn = sqrt(1 &minus; <i>k</i><sup>2</sup>
* sin<sup>2</sup>&phi;).
* @return the periodic function &pi; \e H(&phi;, \e k) / (2 \e H(\e k)) -
* &phi;.
**********************************************************************/
Math::real deltaH(real sn, real cn, real dn) const;
///@}
/** \name Elliptic functions.
**********************************************************************/
///@{
/**
* The Jacobi elliptic functions.
*
* @param[in] x the argument.
* @param[out] sn sn(\e x, \e k).
* @param[out] cn cn(\e x, \e k).
* @param[out] dn dn(\e x, \e k).
**********************************************************************/
void sncndn(real x, real& sn, real& cn, real& dn) const;
/**
* The &Delta; amplitude function.
*
* @param[in] sn sin&phi;.
* @param[in] cn cos&phi;.
* @return &Delta; = sqrt(1 &minus; <i>k</i><sup>2</sup>
* sin<sup>2</sup>&phi;).
**********************************************************************/
Math::real Delta(real sn, real cn) const {
using std::sqrt;
return sqrt(_k2 < 0 ? 1 - _k2 * sn*sn : _kp2 + _k2 * cn*cn);
}
///@}
/** \name Symmetric elliptic integrals.
**********************************************************************/
///@{
/**
* Symmetric integral of the first kind <i>R</i><sub><i>F</i></sub>.
*
* @param[in] x
* @param[in] y
* @param[in] z
* @return <i>R</i><sub><i>F</i></sub>(\e x, \e y, \e z).
*
* <i>R</i><sub><i>F</i></sub> is defined in https://dlmf.nist.gov/19.16.E1
* \f[ R_F(x, y, z) = \frac12
* \int_0^\infty\frac1{\sqrt{(t + x) (t + y) (t + z)}}\, dt, \f]
* where at most one of arguments, \e x, \e y, \e z, can be zero and those
* arguments that are nonzero must be positive. If one of the arguments is
* zero, it is more efficient to call the two-argument version of this
* function with the non-zero arguments.
**********************************************************************/
static real RF(real x, real y, real z);
/**
* Complete symmetric integral of the first kind,
* <i>R</i><sub><i>F</i></sub> with one argument zero.
*
* @param[in] x
* @param[in] y
* @return <i>R</i><sub><i>F</i></sub>(\e x, \e y, 0).
*
* The arguments \e x and \e y must be positive.
**********************************************************************/
static real RF(real x, real y);
/**
* Degenerate symmetric integral of the first kind
* <i>R</i><sub><i>C</i></sub>.
*
* @param[in] x
* @param[in] y
* @return <i>R</i><sub><i>C</i></sub>(\e x, \e y) =
* <i>R</i><sub><i>F</i></sub>(\e x, \e y, \e y).
*
* <i>R</i><sub><i>C</i></sub> is defined in https://dlmf.nist.gov/19.2.E17
* \f[ R_C(x, y) = \frac12
* \int_0^\infty\frac1{\sqrt{t + x}(t + y)}\,dt, \f]
* where \e x &ge; 0 and \e y > 0.
**********************************************************************/
static real RC(real x, real y);
/**
* Symmetric integral of the second kind <i>R</i><sub><i>G</i></sub>.
*
* @param[in] x
* @param[in] y
* @param[in] z
* @return <i>R</i><sub><i>G</i></sub>(\e x, \e y, \e z).
*
* <i>R</i><sub><i>G</i></sub> is defined in Carlson, eq 1.5
* \f[ R_G(x, y, z) = \frac14
* \int_0^\infty[(t + x) (t + y) (t + z)]^{-1/2}
* \biggl(
* \frac x{t + x} + \frac y{t + y} + \frac z{t + z}
* \biggr)t\,dt, \f]
* where at most one of arguments, \e x, \e y, \e z, can be zero and those
* arguments that are nonzero must be positive. See also
* https://dlmf.nist.gov/19.23.E6_5. If one of the arguments is zero, it
* is more efficient to call the two-argument version of this function with
* the non-zero arguments.
**********************************************************************/
static real RG(real x, real y, real z);
/**
* Complete symmetric integral of the second kind,
* <i>R</i><sub><i>G</i></sub> with one argument zero.
*
* @param[in] x
* @param[in] y
* @return <i>R</i><sub><i>G</i></sub>(\e x, \e y, 0).
*
* The arguments \e x and \e y must be positive.
**********************************************************************/
static real RG(real x, real y);
/**
* Symmetric integral of the third kind <i>R</i><sub><i>J</i></sub>.
*
* @param[in] x
* @param[in] y
* @param[in] z
* @param[in] p
* @return <i>R</i><sub><i>J</i></sub>(\e x, \e y, \e z, \e p).
*
* <i>R</i><sub><i>J</i></sub> is defined in https://dlmf.nist.gov/19.16.E2
* \f[ R_J(x, y, z, p) = \frac32
* \int_0^\infty
* [(t + x) (t + y) (t + z)]^{-1/2} (t + p)^{-1}\, dt, \f]
* where \e p > 0, and \e x, \e y, \e z are nonnegative with at most one of
* them being 0.
**********************************************************************/
static real RJ(real x, real y, real z, real p);
/**
* Degenerate symmetric integral of the third kind
* <i>R</i><sub><i>D</i></sub>.
*
* @param[in] x
* @param[in] y
* @param[in] z
* @return <i>R</i><sub><i>D</i></sub>(\e x, \e y, \e z) =
* <i>R</i><sub><i>J</i></sub>(\e x, \e y, \e z, \e z).
*
* <i>R</i><sub><i>D</i></sub> is defined in https://dlmf.nist.gov/19.16.E5
* \f[ R_D(x, y, z) = \frac32
* \int_0^\infty[(t + x) (t + y)]^{-1/2} (t + z)^{-3/2}\, dt, \f]
* where \e x, \e y, \e z are positive except that at most one of \e x and
* \e y can be 0.
**********************************************************************/
static real RD(real x, real y, real z);
///@}
};
} // namespace GeographicLib
#endif // GEOGRAPHICLIB_ELLIPTICFUNCTION_HPP
Constants.hpp
Header for GeographicLib::Constants class.
GEOGRAPHICLIB_EXPORT
#define GEOGRAPHICLIB_EXPORT
Definition: Constants.hpp:67
real
GeographicLib::Math::real real
Definition: GeodSolve.cpp:29
GeographicLib::EllipticFunction
Elliptic integrals and functions.
Definition: EllipticFunction.hpp:63
GeographicLib::EllipticFunction::G
Math::real G() const
Definition: EllipticFunction.hpp:251
GeographicLib::EllipticFunction::H
Math::real H() const
Definition: EllipticFunction.hpp:265
GeographicLib::EllipticFunction::EllipticFunction
EllipticFunction(real k2=0, real alpha2=0)
Definition: EllipticFunction.hpp:90
GeographicLib::EllipticFunction::Pi
Math::real Pi() const
Definition: EllipticFunction.hpp:238
GeographicLib::EllipticFunction::E
Math::real E() const
Definition: EllipticFunction.hpp:203
GeographicLib::EllipticFunction::k2
Math::real k2() const
Definition: EllipticFunction.hpp:158
GeographicLib::EllipticFunction::alphap2
Math::real alphap2() const
Definition: EllipticFunction.hpp:175
GeographicLib::EllipticFunction::Reset
void Reset(real k2=0, real alpha2=0)
Definition: EllipticFunction.hpp:126
GeographicLib::EllipticFunction::Delta
Math::real Delta(real sn, real cn) const
Definition: EllipticFunction.hpp:586
GeographicLib::EllipticFunction::K
Math::real K() const
Definition: EllipticFunction.hpp:191
GeographicLib::EllipticFunction::EllipticFunction
EllipticFunction(real k2, real alpha2, real kp2, real alphap2)
Definition: EllipticFunction.hpp:112
GeographicLib::EllipticFunction::kp2
Math::real kp2() const
Definition: EllipticFunction.hpp:164
GeographicLib::EllipticFunction::KE
Math::real KE() const
Definition: EllipticFunction.hpp:224
GeographicLib::EllipticFunction::alpha2
Math::real alpha2() const
Definition: EllipticFunction.hpp:169
GeographicLib::EllipticFunction::D
Math::real D() const
Definition: EllipticFunction.hpp:216
GeographicLib::Math::real
double real
Definition: Math.hpp:100
GeographicLib
Namespace for GeographicLib.
Definition: Accumulator.cpp:12