#include "sofam.h"
 
void iauPmat76(double date1, double date2, double rmatp[3][3])
/*
**  - - - - - - - - - -
**   i a u P m a t 7 6
**  - - - - - - - - - -
**
**  Precession matrix from J2000 to a specified date, IAU 1976 model.
**
**  This function is part of the International Astronomical Union's
**  SOFA (Standards Of Fundamental Astronomy) software collection.
**
**  Status:  support function.
**
**  Given:
**     date1,date2 double        ending date, TDB (Note 1)
**
**  Returned:
**     rmatp       double[3][3]  precession matrix, J2000 -> date1+date2
**
**  Notes:
**
**  1) The TT date date1+date2 is a Julian Date, apportioned in any
**     convenient way between the two arguments.  For example,
**     JD(TT)=2450123.7 could be expressed in any of these ways,
**     among others:
**
**            date1          date2
**
**         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 resolution.  The MJD method and the date & time methods
**     are both good compromises between resolution and convenience.
**
**  2) The matrix operates in the sense V(date) = RMATP * V(J2000),
**     where the p-vector V(J2000) is with respect to the mean
**     equatorial triad of epoch J2000 and the p-vector V(date)
**     is with respect to the mean equatorial triad of the given
**     date.
**
**  3) Though the matrix method itself is rigorous, the precession
**     angles 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.
**
**  Called:
**     iauPrec76    accumulated precession angles, IAU 1976
**     iauIr        initialize r-matrix to identity
**     iauRz        rotate around Z-axis
**     iauRy        rotate around Y-axis
**     iauCr        copy r-matrix
**
**  References:
**
**     Lieske, J.H., 1979, Astron.Astrophys. 73, 282.
**      equations (6) & (7), p283.
**
**     Kaplan,G.H., 1981. USNO circular no. 163, pA2.
**
**  This revision:  2008 May 24
**
**  Copyright (C) 2008 IAU SOFA Review Board.  See notes at end.
*/
{
   double zeta, z, theta, wmat[3][3];


/* Precession Euler angles, J2000 to specified date. */
   iauPrec76(DJ00, 0.0, date1, date2, &zeta, &z, &theta);
 
/* Form the rotation matrix. */
   iauIr(  wmat);
   iauRz( -zeta, wmat);
   iauRy(  theta, wmat);
   iauRz( -z, wmat);
   iauCr( wmat, rmatp);
 
   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
**
**---------------------------------------------------------------------*/
}