#include "sofa.h"

void iauNut06a(double date1, double date2, double *dpsi, double *deps)
/*
**  - - - - - - - - - -
**   i a u N u t 0 6 a
**  - - - - - - - - - -
**
**  IAU 2000A nutation with adjustments to match the IAU 2006
**  precession.
**
**  Given:
**     date1,date2   double   TT as a 2-part Julian Date (Note 1)
**
**  Returned:
**     dpsi,deps     double   nutation, luni-solar + planetary (Note 2)
**
**  Status:  canonical model.
**
**  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 nutation components in longitude and obliquity are in radians
**     and with respect to the mean equinox and ecliptic of date,
**     IAU 2006 precession model (Hilton et al. 2006, Capitaine et al.
**     2005).
**
**  3) The function first computes the IAU 2000A nutation, then applies
**     adjustments for (i) the consequences of the change in obliquity
**     from the IAU 1980 ecliptic to the IAU 2006 ecliptic and (ii) the
**     secular variation in the Earth's dynamical form factor J2.
**
**  4) The present function provides classical nutation, complementing
**     the IAU 2000 frame bias and IAU 2006 precession.  It delivers a
**     pole which is at current epochs accurate to a few tens of
**     microarcseconds, apart from the free core nutation.
**
**  Called:
**     iauNut00a    nutation, IAU 2000A
**
**  References:
**
**     Chapront, J., Chapront-Touze, M. & Francou, G. 2002,
**     Astron.Astrophys. 387, 700
**
**     Lieske, J.H., Lederle, T., Fricke, W. & Morando, B. 1977,
**     Astron.Astrophys. 58, 1-16
**
**     Mathews, P.M., Herring, T.A., Buffet, B.A. 2002, J.Geophys.Res.
**     107, B4.  The MHB_2000 code itself was obtained on 9th September
**     2002 from ftp//maia.usno.navy.mil/conv2000/chapter5/IAU2000A.
**
**     Simon, J.-L., Bretagnon, P., Chapront, J., Chapront-Touze, M.,
**     Francou, G., Laskar, J. 1994, Astron.Astrophys. 282, 663-683
**
**     Souchay, J., Loysel, B., Kinoshita, H., Folgueira, M. 1999,
**     Astron.Astrophys.Supp.Ser. 135, 111
**
**     Wallace, P.T., "Software for Implementing the IAU 2000
**     Resolutions", in IERS Workshop 5.1 (2002)
**
**  This revision:  2013 June 18
**
**  SOFA release 2020-07-21
**
**  Copyright (C) 2020 IAU SOFA Board.  See notes at end.
*/
{
   double t, fj2, dp, de;


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

/* Factor correcting for secular variation of J2. */
   fj2 = -2.7774e-6 * t;

/* Obtain IAU 2000A nutation. */
   iauNut00a(date1, date2, &dp, &de);

/* Apply P03 adjustments (Wallace & Capitaine, 2006, Eqs.5). */
   *dpsi = dp + dp * (0.4697e-6 + fj2);
   *deps = de + de * fj2;

   return;

/*----------------------------------------------------------------------
**
**  Copyright (C) 2020
**  Standards Of Fundamental Astronomy Board
**  of the International Astronomical Union.
**
**  =====================
**  SOFA Software License
**  =====================
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**
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**--------------------------------------------------------------------*/
}
