#include "sofa.h"

void iauPr00(double date1, double date2, double *dpsipr, double *depspr)
/*
**  - - - - - - - -
**   i a u P r 0 0
**  - - - - - - - -
**
**  Precession-rate part of the IAU 2000 precession-nutation models
**  (part of MHB2000).
**
**  This function is part of the International Astronomical Union's
**  SOFA (Standards Of Fundamental Astronomy) software collection.
**
**  Status:  canonical model.
**
**  Given:
**     date1,date2    double  TT as a 2-part Julian Date (Note 1)
**
**  Returned:
**     dpsipr,depspr  double  precession corrections (Notes 2,3)
**
**  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 precession adjustments are expressed as "nutation
**     components", corrections in longitude and obliquity with respect
**     to the J2000.0 equinox and ecliptic.
**
**  3) Although the precession adjustments are stated to be with respect
**     to Lieske et al. (1977), the MHB2000 model does not specify which
**     set of Euler angles are to be used and how the adjustments are to
**     be applied.  The most literal and straightforward procedure is to
**     adopt the 4-rotation epsilon_0, psi_A, omega_A, xi_A option, and
**     to add dpsipr to psi_A and depspr to both omega_A and eps_A.
**
**  4) This is an implementation of one aspect of the IAU 2000A nutation
**     model, formally adopted by the IAU General Assembly in 2000,
**     namely MHB2000 (Mathews et al. 2002).
**
**  References:
**
**     Lieske, J.H., Lederle, T., Fricke, W. & Morando, B., "Expressions
**     for the precession quantities based upon the IAU (1976) System of
**     Astronomical Constants", Astron.Astrophys., 58, 1-16 (1977)
**
**     Mathews, P.M., Herring, T.A., Buffet, B.A., "Modeling of nutation
**     and precession   New nutation series for nonrigid Earth and
**     insights into the Earth's interior", J.Geophys.Res., 107, B4,
**     2002.  The MHB2000 code itself was obtained on 9th September 2002
**     from ftp://maia.usno.navy.mil/conv2000/chapter5/IAU2000A.
**
**     Wallace, P.T., "Software for Implementing the IAU 2000
**     Resolutions", in IERS Workshop 5.1 (2002).
**
**  This revision:  2013 June 18
**
**  SOFA release 2021-01-25
**
**  Copyright (C) 2021 IAU SOFA Board.  See notes at end.
*/
{
   double t;

/* Precession and obliquity corrections (radians per century) */
   static const double PRECOR = -0.29965 * DAS2R,
                       OBLCOR = -0.02524 * DAS2R;


/* Interval between fundamental epoch J2000.0 and given date (JC). */
   t = ((date1 - DJ00) + date2) / DJC;

/* Precession rate contributions with respect to IAU 1976/80. */
   *dpsipr = PRECOR * t;
   *depspr = OBLCOR * t;

   return;

/*----------------------------------------------------------------------
**
**  Copyright (C) 2021
**  Standards Of Fundamental Astronomy Board
**  of the International Astronomical Union.
**
**  =====================
**  SOFA Software License
**  =====================
**
**  NOTICE TO USER:
**
**  BY USING THIS SOFTWARE YOU ACCEPT THE FOLLOWING SIX TERMS AND
**  CONDITIONS WHICH APPLY TO ITS USE.
**
**  1. The Software is owned by the IAU SOFA Board ("SOFA").
**
**  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 distribute SOFA source code to others,
**     and use and adapt its code and algorithms in your own software,
**     on a world-wide, royalty-free basis.  That portion of your
**     distribution that does not consist of intact and unchanged copies
**     of SOFA source code files is a "derived work" that must comply
**     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 itself constitute software provided by and/or
**        endorsed by SOFA.
**
**     b) The source code of your derived work must contain descriptions
**        of how the derived work is based upon, contains and/or differs
**        from the original SOFA software.
**
**     c) The names of all routines in your derived work shall not
**        include the prefix "iau" or "sofa" or trivial modifications
**        thereof such as changes of case.
**
**     d) The origin of the SOFA components of your derived work must
**        not be misrepresented;  you must not claim that you wrote the
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**        software or algorithms embedded in the SOFA software.
**
**     e) 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.
**
**     Note that, as originally distributed, the SOFA software is
**     intended to be a definitive implementation of the IAU standards,
**     and consequently third-party modifications are discouraged.  All
**     variations, no matter how minor, must be explicitly marked as
**     such, as explained above.
**
**  4. You shall not cause the SOFA software to be brought into
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**
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**
**  6. The provision of any version of the SOFA software under the terms
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*
**  In any published work or commercial product which uses the SOFA
**  software directly, acknowledgement (see www.iausofa.org) is
**  appreciated.
**
**  Correspondence concerning SOFA software should be addressed as
**  follows:
**
**      By email:  sofa@ukho.gov.uk
**      By post:   IAU SOFA Center
**                 HM Nautical Almanac Office
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**
**--------------------------------------------------------------------*/
}
