#include "erfa.h"
void eraLtpequ(double epj, double veq[3])
/*
** - - - - - - - - - -
** e r a L t p e q u
** - - - - - - - - - -
**
** Long-term precession of the equator.
**
** Given:
** epj double Julian epoch (TT)
**
** Returned:
** veq double[3] equator pole unit vector
**
** Notes:
**
** 1) The returned vector is with respect to the J2000.0 mean equator
** and equinox.
**
** 2) The Vondrak et al. (2011, 2012) 400 millennia precession model
** agrees with the IAU 2006 precession at J2000.0 and stays within
** 100 microarcseconds during the 20th and 21st centuries. It is
** accurate to a few arcseconds throughout the historical period,
** worsening to a few tenths of a degree at the end of the
** +/- 200,000 year time span.
**
** References:
**
** Vondrak, J., Capitaine, N. and Wallace, P., 2011, New precession
** expressions, valid for long time intervals, Astron.Astrophys. 534,
** A22
**
** Vondrak, J., Capitaine, N. and Wallace, P., 2012, New precession
** expressions, valid for long time intervals (Corrigendum),
** Astron.Astrophys. 541, C1
**
** Copyright (C) 2013-2016, NumFOCUS Foundation.
** Derived, with permission, from the SOFA library. See notes at end of file.
*/
{
/* Polynomial coefficients */
enum { NPOL = 4 };
static const double xypol[2][NPOL] = {
{ 5453.282155,
0.4252841,
-0.00037173,
-0.000000152},
{-73750.930350,
-0.7675452,
-0.00018725,
0.000000231}
};
/* Periodic coefficients */
static const double xyper[][5] = {
{ 256.75, -819.940624,75004.344875,81491.287984, 1558.515853},
{ 708.15,-8444.676815, 624.033993, 787.163481, 7774.939698},
{ 274.20, 2600.009459, 1251.136893, 1251.296102,-2219.534038},
{ 241.45, 2755.175630,-1102.212834,-1257.950837,-2523.969396},
{2309.00, -167.659835,-2660.664980,-2966.799730, 247.850422},
{ 492.20, 871.855056, 699.291817, 639.744522, -846.485643},
{ 396.10, 44.769698, 153.167220, 131.600209,-1393.124055},
{ 288.90, -512.313065, -950.865637, -445.040117, 368.526116},
{ 231.10, -819.415595, 499.754645, 584.522874, 749.045012},
{1610.00, -538.071099, -145.188210, -89.756563, 444.704518},
{ 620.00, -189.793622, 558.116553, 524.429630, 235.934465},
{ 157.87, -402.922932, -23.923029, -13.549067, 374.049623},
{ 220.30, 179.516345, -165.405086, -210.157124, -171.330180},
{1200.00, -9.814756, 9.344131, -44.919798, -22.899655}
};
static const int NPER = (int) ( sizeof xyper / 5 / sizeof (double) );
/* Miscellaneous */
int i;
double t, x, y, w, a, s, c;
/* Centuries since J2000. */
t = ( epj - 2000.0 ) / 100.0;
/* Initialize X and Y accumulators. */
x = 0.0;
y = 0.0;
/* Periodic terms. */
w = ERFA_D2PI * t;
for ( i = 0; i < NPER; i++ ) {
a = w / xyper[i][0];
s = sin(a);
c = cos(a);
x += c*xyper[i][1] + s*xyper[i][3];
y += c*xyper[i][2] + s*xyper[i][4];
}
/* Polynomial terms. */
w = 1.0;
for ( i = 0; i < NPOL; i++ ) {
x += xypol[0][i]*w;
y += xypol[1][i]*w;
w *= t;
}
/* X and Y (direction cosines). */
x *= ERFA_DAS2R;
y *= ERFA_DAS2R;
/* Form the equator pole vector. */
veq[0] = x;
veq[1] = y;
w = 1.0 - x*x - y*y;
veq[2] = w < 0.0 ? 0.0 : sqrt(w);
}
/*----------------------------------------------------------------------
**
**
** Copyright (C) 2013-2016, NumFOCUS Foundation.
** All rights reserved.
**
** This library is derived, with permission, from the International
** Astronomical Union's "Standards of Fundamental Astronomy" library,
** available from http://www.iausofa.org.
**
** The ERFA version is intended to retain identical functionality to
** the SOFA library, but made distinct through different function and
** file names, as set out in the SOFA license conditions. The SOFA
** original has a role as a reference standard for the IAU and IERS,
** and consequently redistribution is permitted only in its unaltered
** state. The ERFA version is not subject to this restriction and
** therefore can be included in distributions which do not support the
** concept of "read only" software.
**
** Although the intent is to replicate the SOFA API (other than
** replacement of prefix names) and results (with the exception of
** bugs; any that are discovered will be fixed), SOFA is not
** responsible for any errors found in this version of the library.
**
** If you wish to acknowledge the SOFA heritage, please acknowledge
** that you are using a library derived from SOFA, rather than SOFA
** itself.
**
**
** TERMS AND CONDITIONS
**
** Redistribution and use in source and binary forms, with or without
** modification, are permitted provided that the following conditions
** are met:
**
** 1 Redistributions of source code must retain the above copyright
** notice, this list of conditions and the following disclaimer.
**
** 2 Redistributions in binary form must reproduce the above copyright
** notice, this list of conditions and the following disclaimer in
** the documentation and/or other materials provided with the
** distribution.
**
** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
** the International Astronomical Union nor the names of its
** contributors may be used to endorse or promote products derived
** from this software without specific prior written permission.
**
** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
** POSSIBILITY OF SUCH DAMAGE.
**
*/