src/Marando/IAU/iauPr00.php
public static function Pr00($date1, $date2, &$dpsipr, &$depspr) {
    $t;

    /* Precession and obliquity corrections (radians per century) */
    $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;
  }
public static function Pr00($date1, $date2, &$dpsipr, &$depspr) {
    $t;

    /* Precession and obliquity corrections (radians per century) */
    $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;
  }
public static function Pr00 ( $ date1 , $ date2 , & $ dpsipr , & $ depspr ) { $ t ; /* Precession and obliquity corrections (radians per century) */ $ 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 ; }
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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 2015-02-09

Copyright (C) 2015 IAU SOFA Board.  See notes at end.
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