rfa 0.5.9

A port ERFA to Rust.
Documentation 
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use super::{pnm06a::*, bpn2xy::*, s06::*};
///  For a given TT date, compute the X,Y coordinates of the Celestial
///  Intermediate Pole and the CIO locator s, using the IAU 2006
///  precession and IAU 2000A nutation models.
///
///  Given:
///     date1,date2  double  TT as a 2-part Julian Date (Note 1)
///
///  Returned:
///     x,y          double  Celestial Intermediate Pole (Note 2)
///     s            double  the CIO locator s (Note 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 Celestial Intermediate Pole coordinates are the x,y components
///     of the unit vector in the Geocentric Celestial Reference System.
///
///  3) The CIO locator s (in radians) positions the Celestial
///     Intermediate Origin on the equator of the CIP.
///
///  4) Series-based solutions for generating X and Y are also available:
///     see Capitaine & Wallace (2006) and eraXy06.
///
///  Called:
///     eraPnm06a    classical NPB matrix, IAU 2006/2000A
///     eraBpn2xy    extract CIP X,Y coordinates from NPB matrix
///     eraS06       the CIO locator s, given X,Y, IAU 2006
///
///  References:
///
///     Capitaine, N. & Wallace, P.T., 2006, Astron.Astrophys. 450, 855
///
///     Wallace, P.T. & Capitaine, N., 2006, Astron.Astrophys. 459, 981
///
///  This revision:  2021 May 11
pub fn xys06a(date1: f64, date2: f64,
    x: &mut f64, y: &mut f64, s: &mut f64)
{
    let mut rbpn = [[0.0; 3]; 3];
 
 
 /* Form the bias-precession-nutation matrix, IAU 2006/2000A. */
    pnm06a(date1, date2, &mut rbpn);
 
 /* Extract X,Y. */
    bpn2xy(&rbpn, x, y);
 
 /* Obtain s. */
    *s = s06(date1, date2, *x, *y);
 
 /* Finished. */
 
 }