sofars 0.6.0

Pure Rust implementation of the IAU SOFA library
Documentation 
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use super::ee00;
use crate::pnp::{nut00b, obl80, pr00};

///  Equation of the equinoxes, IAU 2000B
///
///  Equation of the equinoxes, compatible with IAU 2000 resolutions but
///  using the truncated nutation model IAU 2000B.
///
///  This function is part of the International Astronomical Union's
///  SOFA (Standards of Fundamental Astronomy) software collection.
///
///  Status:  support function.
///
///  Given:
///     date1,date2  double    TT as a 2-part Julian Date (Note 1)
///
///  Returned (function value):
///                  double    equation of the equinoxes (Note 2)
///
///  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 result, which is in radians, operates in the following sense:
///
///        Greenwich apparent ST = GMST + equation of the equinoxes
///
///  3) The result is compatible with the IAU 2000 resolutions except
///     that accuracy has been compromised (1 mas) for the sake of speed.
///     For further details, see McCarthy & Luzum (2003), IERS
///     Conventions 2003 and Capitaine et al. (2003).
///
///  Called:
///  ```
///     iauPr00      IAU 2000 precession adjustments
///     iauObl80     mean obliquity, IAU 1980
///     iauNut00b    nutation, IAU 2000B
///     iauEe00      equation of the equinoxes, IAU 2000
///  ```
///  References:
///
///     Capitaine, N., Wallace, P.T. and McCarthy, D.D., "Expressions to
///     implement the IAU 2000 definition of UT1", Astronomy &
///     Astrophysics, 406, 1135-1149 (2003)
///
///     McCarthy, D.D. & Luzum, B.J., "An abridged model of the
///     precession-nutation of the celestial pole", Celestial Mechanics &
///     Dynamical Astronomy, 85, 37-49 (2003)
///
///     McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
///     IERS Technical Note No. 32, BKG (2004)
pub fn ee00b(date1: f64, date2: f64) -> f64 {
    let (_, depspr) = pr00(date1, date2);

    // Mean obliquity, consistent with IAU 2000 precession-nutation.
    let epsa = obl80(date1, date2) + depspr;

    // Nutation in longitude.
    let (dpsi, _) = nut00b(date1, date2);

    // Equation of the equinoxes.
    let ee = ee00(date1, date2, epsa, dpsi);

    ee
}