rfa 0.5.9

A port ERFA to Rust.
Documentation 
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use super::{ pnm00a::pnm00a, s00::s00, bpn2xy::*,};
///  The CIO locator s, positioning the Celestial Intermediate Origin on
///  the equator of the Celestial Intermediate Pole, using the IAU 2000A
///  precession-nutation model.
///
///  Given:
///   * date1,date2  TT as a 2-part Julian Date (Note 1)
///
///  Returned (function value):
///   * the CIO locator s in radians (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 CIO locator s is the difference between the right ascensions
///     of the same point in two systems.  The two systems are the GCRS
///     and the CIP,CIO, and the point is the ascending node of the
///     CIP equator.  The CIO locator s remains a small fraction of
///     1 arcsecond throughout 1900-2100.
///
///  3) The series used to compute s is in fact for s+XY/2, where X and Y
///     are the x and y components of the CIP unit vector;  this series
///     is more compact than a direct series for s would be.  The present
///     function uses the full IAU 2000A nutation model when predicting
///     the CIP position.  Faster results, with no significant loss of
///     accuracy, can be obtained via the function eraS00b, which uses
///     instead the IAU 2000B truncated model.
///
/// # Called:
///    * pnnm00a    classical NPB matrix, IAU 2000A
///    * bnp2xy    extract CIP X,Y from the BPN matrix
///    * s00       the CIO locator s, given X,Y, IAU 2000A
///
/// # References:
///
///     Capitaine, N., Chapront, J., Lambert, S. and Wallace, P.,
///     "Expressions for the Celestial Intermediate Pole and Celestial
///     Ephemeris Origin consistent with the IAU 2000A precession-
///     nutation model", Astron.Astrophys. 400, 1145-1154 (2003)
///
///     n.b. The celestial ephemeris origin (CEO) was renamed "celestial
///          intermediate origin" (CIO) by IAU 2006 Resolution 2.
///
///     McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
///     IERS Technical Note No. 32, BKG (2004)
///
///  This revision:  2021 May 11
pub fn s00a(date1: f64, date2: f64)->f64
{
    let mut  rbpn = [[0.0; 3]; 3];
    let mut x =0.0; let mut y =0.0; 
 
 /* Bias-precession-nutation-matrix, IAU 2000A. */
    pnm00a(date1, date2, &mut rbpn);
 
 /* Extract the CIP coordinates. */
    bpn2xy(&mut rbpn, &mut x, &mut y);
 
 /* Compute the CIO locator s, given the CIP coordinates. */
    s00(date1, date2, x, y)
 
 /* Finished. */
 
 }