#include "sofam.h"
void iauPrec76(double ep01, double ep02, double ep11, double ep12,
double *zeta, double *z, double *theta)
/*
** - - - - - - - - - -
** i a u P r e c 7 6
** - - - - - - - - - -
**
** IAU 1976 precession model.
**
** This function forms the three Euler angles which implement general
** precession between two epochs, using the IAU 1976 model (as for
** the FK5 catalog).
**
** This function is part of the International Astronomical Union's
** SOFA (Standards Of Fundamental Astronomy) software collection.
**
** Status: canonical model.
**
** Given:
** ep01,ep02 double TDB starting epoch (Note 1)
** ep11,ep12 double TDB ending epoch (Note 1)
**
** Returned:
** zeta double 1st rotation: radians cw around z
** z double 3rd rotation: radians cw around z
** theta double 2nd rotation: radians ccw around y
**
** Notes:
**
** 1) The epochs ep01+ep02 and ep11+ep12 are Julian Dates, apportioned
** in any convenient way between the arguments epn1 and epn2. For
** example, JD(TDB)=2450123.7 could be expressed in any of these
** ways, among others:
**
** epn1 epn2
**
** 2450123.7 0.0 (JD method)
** 2451545.0 -1421.3 (J2000 method)
** 2400000.5 50123.2 (MJD method)
** 2450123.5 0.2 (date & time method)
**
** The JD method is the most natural and convenient to use in cases
** where the loss of several decimal digits of resolution is
** acceptable. The J2000 method is best matched to the way the
** argument is handled internally and will deliver the optimum
** optimum resolution. The MJD method and the date & time methods
** are both good compromises between resolution and convenience.
** The two epochs may be expressed using different methods, but at
** the risk of losing some resolution.
**
** 2) The accumulated precession angles zeta, z, theta are expressed
** through canonical polynomials which are valid only for a limited
** time span. In addition, the IAU 1976 precession rate is known to
** be imperfect. The absolute accuracy of the present formulation
** is better than 0.1 arcsec from 1960AD to 2040AD, better than
** 1 arcsec from 1640AD to 2360AD, and remains below 3 arcsec for
** the whole of the period 500BC to 3000AD. The errors exceed
** 10 arcsec outside the range 1200BC to 3900AD, exceed 100 arcsec
** outside 4200BC to 5600AD and exceed 1000 arcsec outside 6800BC to
** 8200AD.
**
** 3) The three angles are returned in the conventional order, which
** is not the same as the order of the corresponding Euler
** rotations. The precession matrix is
** R_3(-z) x R_2(+theta) x R_3(-zeta).
**
** Reference:
**
** Lieske, J.H., 1979, Astron.Astrophys. 73, 282, equations
** (6) & (7), p283.
**
** This revision: 2008 May 24
**
** Copyright (C) 2008 IAU SOFA Review Board. See notes at end.
*/
{
double t0, t, tas2r, w;
/* Interval between fundamental epoch J2000.0 and beginning epoch (JC). */
t0 = ((ep01 - DJ00) + ep02) / DJC;
/* Interval over which precession required (JC). */
t = ((ep11 - ep01) + (ep12 - ep02)) / DJC;
/* Euler angles. */
tas2r = t * DAS2R;
w = 2306.2181 + (1.39656 - 0.000139 * t0) * t0;
*zeta = (w + ((0.30188 - 0.000344 * t0) + 0.017998 * t) * t) * tas2r;
*z = (w + ((1.09468 + 0.000066 * t0) + 0.018203 * t) * t) * tas2r;
*theta = ((2004.3109 + (-0.85330 - 0.000217 * t0) * t0)
+ ((-0.42665 - 0.000217 * t0) - 0.041833 * t) * t) * tas2r;
return;
/*-----------------------------------------------------------------------
**
** Copyright (C) 2008
** Standards Of Fundamental Astronomy Review Board
** of the International Astronomical Union.
**
** =====================
** SOFA Software License
** =====================
**
** NOTICE TO USER:
**
** BY USING THIS SOFTWARE YOU ACCEPT THE FOLLOWING TERMS AND CONDITIONS
** WHICH APPLY TO ITS USE.
**
** 1. The Software is owned by the IAU SOFA Review Board ("the Board").
**
** 2. Permission is granted to anyone to use the SOFA software for any
** purpose, including commercial applications, free of charge and
** without payment of royalties, subject to the conditions and
** restrictions listed below.
**
** 3. You (the user) may copy and adapt the SOFA software and its
** algorithms for your own purposes and you may copy and distribute
** a resulting "derived work" to others on a world-wide, royalty-free
** basis, provided that the derived work complies with the following
** requirements:
**
** a) Your work shall be marked or carry a statement that it (i) uses
** routines and computations derived by you from software provided
** by SOFA under license to you; and (ii) does not contain
** software provided by SOFA or software that has been distributed
** by or endorsed by SOFA.
**
** b) The source code of your derived work must contain descriptions
** of how the derived work is based upon and/or differs from the
** original SOFA software.
**
** c) The name(s) of all routine(s) that you distribute shall differ
** from the SOFA names, even when the SOFA content has not been
** otherwise changed.
**
** d) The routine-naming prefix "iau" shall not be used.
**
** e) The origin of the SOFA components of your derived work must not
** be misrepresented; you must not claim that you wrote the
** original software, nor file a patent application for SOFA
** software or algorithms embedded in the SOFA software.
**
** f) These requirements must be reproduced intact in any source
** distribution and shall apply to anyone to whom you have granted
** a further right to modify the source code of your derived work.
**
** 4. In any published work or commercial products which includes
** results achieved by using the SOFA software, you shall acknowledge
** that the SOFA software was used in obtaining those results.
**
** 5. You shall not cause the SOFA software to be brought into
** disrepute, either by misuse, or use for inappropriate tasks, or by
** inappropriate modification.
**
** 6. The SOFA software is provided "as is" and the Board makes no
** warranty as to its use or performance. The Board does not and
** cannot warrant the performance or results which the user may obtain
** by using the SOFA software. The Board makes no warranties, express
** or implied, as to non-infringement of third party rights,
** merchantability, or fitness for any particular purpose. In no
** event will the Board be liable to the user for any consequential,
** incidental, or special damages, including any lost profits or lost
** savings, even if a Board representative has been advised of such
** damages, or for any claim by any third party.
**
** 7. The provision of any version of the SOFA software under the terms
** and conditions specified herein does not imply that future
** versions will also be made available under the same terms and
** conditions.
**
** Correspondence concerning SOFA software should be addressed as
** follows:
**
** Internet email: sofa@rl.ac.uk
** Postal address: IAU SOFA Center
** Rutherford Appleton Laboratory
** Chilton, Didcot, Oxon OX11 0QX
** United Kingdom
**
**---------------------------------------------------------------------*/
}